Add config option to project to allow custom .gitlab-ci.yml path

What does this MR do?

Adds option to project to configure the path to the .gitlab-ci.yml file

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

What are the relevant issue numbers?

• #15041 (moved)
• Closes #32815 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

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