Validate FK push_event_payloads#project_id

What does this MR do and why?

Validate FK push_event_payloads#project_id

Addresses #561065 (closed)

Follows up on !201179 (merged) && !201993 (merged)

Validating the FK constraint synchronously for all instances now that it's been completed asynchronously on gitlab.com

Changelog: other

MR acceptance checklist

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