Add support for max_job_timeout parameter in registration

What does this MR do?

Adds support for maximum_job_timeout parameter on Registration API.

Why was this MR needed?

This is Runner's part of gitlab-ce!17221.

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?

gitlab-ce#43426