Groups - README

What does this MR do and why?

Built off the base MR from @peterhegman: !110943 (closed)
Closes #392015 (closed)

This change hooks up the ability to display a README on the Group Information page via a specially named project gitlab-profile.

This is behind the feature flag (:show_group_readme)

Screenshots or screen recordings

	w/ README Project	w/o README Project
Group
Subgroup

How to set up and validate locally

1. Enable the Feature Flag Feature.enable(:show_group_readme)
2. I've had issues lately with FF caching, I'd suggest maybe restarting GDK
3. Go to a Group or Subgroup
4. Create a project named exactly gitlab-profile
5. Add a README.md to the project
6. Go back to the Group Information page
7. Ensure README.md is present under the list of Projects/Subgroups

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #392015 (closed)