Implement MVP for content repos

[schnatterer]

Provide content.repos in config that allows for configuring additional repos into GOP.
This allows for

• adding new applications/cluster-resources
• adding tenants
• deploying GOP with specific turnkey gitops-pipelines
• changing existing content

In the long run, we can remove our hard-coded example apps from the content and make them into a configuration.

content:
  repos:
    - url: 'https://example.org'
      username: xyz
      password: abc
      templating: true
      folderBased: true # target not needed
    - url: https://github.com/cloudogu/spring-petclinic
      target: example-tenant/petclinic
      ref: b0738b2
        ref: feature/gitops_ready
      - url: https://github.com/cloudogu/gitops-build-lib
        target: 3rd-party-dependencies/gitops-build-lib
      - url: https://github.com/cloudogu/ces-build-lib
        target: 3rd-party-dependencies/ces-build-lib
      - url: https://github.com/cloudogu/spring-boot-helm-chart
        target: 3rd-party-dependencies/spring-boot-helm-chart
        ref: 0.4.0 
  namespaces: 
    - example-tenant-staging
    - example-tenant-production
  examples: true