Combine Deploy Keys and Push Rules and Mirror Repository and Protect Branches settings pages

Resources

PM @victorwu | UX @tauriedavis

Background

Part of #23007 (closed).

Scope for this issue

For a given project, combine the existing pages into a single page.
- For EE:
  - Deploy Keys
  - Push Rules
  - Mirror Repository
  - Protect Branches
For CE:
- Deploy Keys
- Push Rules
Call this single page the Repository page.
Update the gear/cog navigation. Combine the above navigation menu items into one menu item called Repository.