Resolve "Project option to allow customizing CI/CD config path"

What does this MR do?

Add an option to customize CI/CD config path (default .gitlab-ci.yml)

Why was this MR needed?

This is a follow up from !5682 (closed), please check the description and discussion there.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• 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

What are the relevant issue numbers?

Closes #32815 (closed)

/cc @muteor