[Backport] move hardcoded MIME types from class private to DI configuration

[gelanivishal]

Original Pull Request

#18365

Description

With this fix, developers can add custom catalog image types like SVG from di.xml configuration.
In Catalog ImageUploader allowed extensions can be customized, but allowed mime types are hardcoded in the class into a private property. (with no getter method). This PR solves this limitation.

[magento-engcom-team]

Hi @gelanivishal. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me $VERSION instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[larsroettig]

@magento-engcom-team give me test instance

[magento-engcom-team]

Hi @larsroettig. Thank you for your request. I'm working on Magento instance for you

[magento-engcom-team]

Hi @larsroettig, here is your new Magento instance.
Admin access: http://ec2-34-228-235-121.compute-1.amazonaws.com/pr-18662//admin
Login: admin Password: 123123q

[larsroettig]

• CodeReview
• Maunal Testing Backend

[magento-engcom-team]

Hi @larsroettig, thank you for the review.
ENGCOM-3208 has been created to process this Pull Request

[magento-engcom-team]

Hi @orlangur, thank you for the review.
ENGCOM-3208 has been created to process this Pull Request

[magento-engcom-team]

Hi @gelanivishal. Thank you for your contribution.
We will aim to release these changes as part of 2.2.8.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.