Add foreign key constraints to ci_runners_e59bb2812d partitions

What does this MR do and why?

This MR is the first MR of a series of MRs that aim to replace the current ci_runners/ci_runner_machines tables with their partitioned versions. The complete flow was tested on a spike MR, and is roughly the following:

1. !180721 (merged) Add foreign key constraints to ci_runners_e59bb2812d partitions ⬅️ This MR
2. !180729 (closed) Index ci_running_builds on runner_id, runner_type
3. Add LFK from ci_running_builds to ci_runners_e59bb2812d
4. Replace ci_runners with partitioned table
5. Track ci_instance_runners deletions
6. Replace ci_runner_machines with partitioned table

Changelog: other

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• Replace ci_runners with partitioned table (#504963 - closed)
• Draft: Spike for replacement of partitioned run... (!179605 - closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.