Rename to gitlab runner

WARNING

This MR introduces a change that - if merged in wrong moment - is breaking a lot of things. Don't merge this without getting familiar with #1195 (closed) and a migration plan that will be added there!

What does this MR do?

Renames all usages of gitlab-ci-multi-runner to gitlab-runner (which includes changes in DEB/RPM packages configuration etc.)

Why was this MR needed?

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

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

Part of #1195 (closed)