Add overview and use cases for MR-related docs

username-removed-236961 requested to merge docs/overview-features-5-ee into master

See the general Documentation guidelines

What does this MR do?

Adds overview and use cases for:

  • Merge requests
  • Merge request approvals
  • Multi-Project Pipeline Graphs (new doc)
  • Code Quality reports

When approved:


Edited by username-removed-236961

Merge request reports