Update runner version only when updating contacted_at

What does this MR do?

Improves how we update runners table, especially the version.

This is another round of improvements to reduce number of ci_runners updates.

I did make contacted_at to be updated more often (on average every 15 minutes). We will also update version information in one go to solve: https://gitlab.com/gitlab-org/gitlab-ce/issues/22206

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 merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Improves: https://gitlab.com/gitlab-org/gitlab-ce/issues/22590 Solves: https://gitlab.com/gitlab-org/gitlab-ce/issues/22206