ENH: Add a structured template for issues

.github/ISSUE_TEMPLATE/bug_report.yml

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+name: "\U0001F41B Bug Report"
+description: If you are pretty sure you are getting a bug, please create a report to help us improve InnerEye-DeepLearning
+labels: ["bug"]
+
+body:
+  - type: checkboxes
+    attributes:
+      label: Is there an existing issue for this?
+      description: Please search to see if an issue already exists for the bug you encountered.
+      options:
+      - label: I have searched the existing issues
+        required: true
+
+  - type: textarea
+    id: summary
+    attributes:
+      label: Bug summary
+      description: Please provide 1-2 short sentences that succinctly describe the bug.
+    validations:
+      required: true
+
+  - type: textarea
+    id: reproduction
+    attributes:
+      label: Code for reproduction
+      description: If applicable, please provide a [minimum self-contained example](https://stackoverflow.com/help/minimal-reproducible-example). It will be automatically formatted.
+      placeholder: Your code here
+      render: Python
+    validations:
+      required: true
+
+  - type: textarea
+    id: actual
+    attributes:
+      label: Actual outcome
+      description: Please describe the outcome of running the above code. Paste any error messages in the section below, not here.
+    validations:
+      required: true
+
+  - type: textarea
+    id: logs
+    attributes:
+      label: Error messages
+      description: Please copy and paste any relevant log output. Paste the full error traceback, not just the last error. It will be automatically formatted.
+      placeholder: Your errors here
+      render: python-traceback
+
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected outcome
+      description: Please provide a description (or visual example) of the expected outcome from the code snippet.
+    validations:
+      required: true
+
+  - type: textarea
+    id: system
+    attributes:
+      label: System info
+      description: |
+        Please describe the operating system that you are using, your Conda environment (by running `conda env export`)
+        and the `git` commit hash (version) of the InnerEye toolbox that you are using. To get the latter, please run:
+
+        ```shell
+        git rev-parse --short HEAD
+        ```
+      placeholder: Your system info (OS version, InnerEye commit hash, Result of `conda env export`)

.github/ISSUE_TEMPLATE/config.yml

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+blank_issues_enabled: true
+contact_links:
+  - name: ❓ Discussions tab
+    url: https://github.com/microsoft/InnerEye-DeepLearning/discussions/new
+    about: Ask and answer InnerEye-related questions or start a general discussion

.github/ISSUE_TEMPLATE/documentation_issue.yml

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+name: "\U0001F4D2 Documentation Problem"
+description: If the documentation is unclear or missing information, please create a report to help us improve InnerEye-DeepLearning
+labels: ["documentation"]
+
+body:
+  - type: checkboxes
+    attributes:
+      label: Is there an existing issue for this?
+      description: Please search to see if an issue already exists for the problem you encountered.
+      options:
+      - label: I have searched the existing issues
+        required: true
+
+  - type: textarea
+    id: summary
+    attributes:
+      label: Issue summary
+      description: Please provide 1-2 short sentences describing where the documentation should be improved. If applicable,
+        please provide the URL of the file that needs updating.
+      placeholder: Description of where an update is needed, URL of the file if possible.
+    validations:
+      required: true
+
+  - type: textarea
+    id: expected
+    attributes:
+      label: What documentation should be provided?
+      description: Please provide a description of what information should be captured or corrected in the documentation.
+    validations:
+      required: true

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: "\U0001F680 Feature Request"
+about: Submit a proposal/request for a new InnerEye feature
+title: ''
+labels: 'enhancement'
+assignees: ''
+
+---
+
+**🚀 Feature**
+<!-- A clear and concise description of the feature proposal -->
+
+**Motivation**
+
+<!-- Please outline the motivation for the proposal. Is your feature request related to a problem? e.g., I'm always frustrated when [...]. If this is related to another GitHub issue, please link here too -->
+
+**Pitch**
+
+<!-- A clear and concise description of what you want to happen. -->
+
+**Alternatives**
+
+<!-- A clear and concise description of any alternative solutions or features you've considered, if any. -->
+
+**Additional context**
+
+<!-- Add any other context or screenshots about the feature request here. -->

.github/ISSUE_TEMPLATE/not_working.yml

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+name: "\U00002757 Something is not working"
+description: >
+  If something is not working as expected but you're not sure if it's a bug,
+  please follow the instructions in this template.
+
+body:
+  - type: checkboxes
+    attributes:
+      label: Is there an existing issue for this?
+      description: Please search to see if an issue already exists for the problem you encountered.
+      options:
+      - label: I have searched the existing issues
+        required: true
+
+  - type: textarea
+    id: summary
+    attributes:
+      label: Problem summary
+      description: Please provide 1-2 short sentences that succinctly describe the problem.
+    validations:
+      required: true
+
+  - type: textarea
+    id: reproduction
+    attributes:
+      label: Code for reproduction
+      description: >
+        If applicable, please provide a [minimum self-contained example](https://stackoverflow.com/help/minimal-reproducible-example).
+        It will be automatically formatted.
+        Here's another useful resource: [How To Ask Questions The Smart Way](http://www.catb.org/~esr/faqs/smart-questions.html).
+      placeholder: Your code here
+      render: Python
+    validations:
+      required: true
+
+  - type: textarea
+    id: actual
+    attributes:
+      label: Actual outcome
+      description: Please describe the outcome of running the above code.
+    validations:
+      required: true
+
+  - type: textarea
+    id: logs
+    attributes:
+      label: Error messages
+      description: >
+        Please copy and paste any relevant log output.
+        Paste the full error traceback, not just the last error.
+      placeholder: Your errors here
+
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected outcome
+      description: >
+        Please provide a description (or visual example) of the expected outcome
+        from the code snippet.
+    validations:
+      required: true
+
+  - type: textarea
+    id: system
+    attributes:
+      label: System info
+      description: |
+        Please describe the operating system that you are using, your Conda environment (by running `conda env export`)
+        and the `git` commit hash (version) of the InnerEye toolbox that you are using. To get the latter, please run:
+
+        ```shell
+        git rev-parse --short HEAD
+        ```
+      placeholder: Your system info (OS version, InnerEye commit hash, Result of `conda env export`)