Asynchronous validation of `finding_id` foreign key on vulnerabilities

What does this MR do and why?

Synchronous migration will be added in #425409 (closed)

How to set up and validate locally

1. Test database FK changes locally

Migration Output

bundle exec rails db:migrate

~/gitlab-development-kit/gitlab$ bundle exec rails db:migrate
main: == [advisory_lock_connection] object_id: 183100, pg_backend_pid: 128883
main: == 20231225070431 AsyncValidateFindingIdOnVulnerabilities: migrating ==========
main: == 20231225070431 AsyncValidateFindingIdOnVulnerabilities: migrated (0.0037s) =

main: == [advisory_lock_connection] object_id: 183100, pg_backend_pid: 128883
ci: == [advisory_lock_connection] object_id: 183200, pg_backend_pid: 128885
ci: == 20231225070431 AsyncValidateFindingIdOnVulnerabilities: migrating ==========
ci: == 20231225070431 AsyncValidateFindingIdOnVulnerabilities: migrated (0.0081s) =

ci: == [advisory_lock_connection] object_id: 183200, pg_backend_pid: 128885

bundle exec rails db:rollback:ci

~/gitlab-development-kit/gitlab$ bundle exec rails db:rollback:ci
ci: == [advisory_lock_connection] object_id: 182380, pg_backend_pid: 129776
ci: == 20231225070431 AsyncValidateFindingIdOnVulnerabilities: reverting ==========
ci: == 20231225070431 AsyncValidateFindingIdOnVulnerabilities: reverted (0.0245s) =

ci: == [advisory_lock_connection] object_id: 182380, pg_backend_pid: 129776

bundle exec rails db:rollback:main

~/gitlab-development-kit/gitlab$ bundle exec rails db:rollback:main
main: == [advisory_lock_connection] object_id: 182440, pg_backend_pid: 129377
main: == 20231225070431 AsyncValidateFindingIdOnVulnerabilities: reverting ==========
main: == 20231225070431 AsyncValidateFindingIdOnVulnerabilities: reverted (0.0217s) =

main: == [advisory_lock_connection] object_id: 182440, pg_backend_pid: 129377

Screenshots

results of \d+ vulnerabilities before/after running migration locally

before	after

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #418972 (closed)