WIP: PoC: How to present junit.xml

What does this MR do?

This merge request is for brainstorming the backend~frontend architecture of presenting JUnit test reports. So we can be confident that passing gzip is the right decision in 11.1.

This merge request is not be merged in 11.1. We have to rework in 11.2.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Related: https://gitlab.com/gitlab-org/gitlab-ce/issues/46809