WIP: Protected runner executes jobs on protected branch [Solution 2]

What does this MR do?

This MR is continued from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13192. To accomplish this feature, we need to implement a mechanism for "Protected runner executes jobs on protected branch. Unprotected runner executes jobs on unprotected branch". However, there is a technical challenge that ci_builds doesn't have data whether the ref is protected or not.

This MR addresses the challenge with Solution 2.

Solution 2. Executes protected_for? greedily to each build from builds_for_shared_runner or builds_for_specific_runner.

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13192#note_36332863

• Pro

• Simple

• Don't alter column on ci_pipelines

• Con

• Slow

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

Why was this MR needed?

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
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• 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?

• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13192
• Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/33281
• Solution 1 => https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13194