Add runner_machines relationships

MR chain breakdown:

Sequence	MR
👉 1	Add runner_machines relationships (!109980 - merged)
2	Add logic to create ci_runner_machine based on ... (!109983 - merged)
3	Implement Ci::RunnerMachine#heartbeat (!109985 - merged)

Part of Use runner token + `system_id` JSON parameters ... (#387181 - closed)

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR adds the relationships between ci_builds/ci_runner_machines/ci_runner_versions.

Screenshots or screen recordings

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header	header
Ci::RunnerMachine relationships
Ci::Build relationships
Ci::RunnerVersion relationships

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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