Unify projects search by removing /projects/:search endpoint

Removes /projects/:search endpoint (avoiding duplicated behavior with /projects?search=x).

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• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

Closes #22007 (closed)