Address the Primary Key Overflow risk for the geo_job_artifact_deleted_events table - Step 2: Finalize background migrations and swap columns

With #331789 (closed) we have started the process of converting geo_job_artifact_deleted_events.job_artifact_id to bigint (int8), as it references ci_job_artifacts.id.

In this issue we'll address the second step of the process:

1. Ensure the migration of job_artifact_id to job_artifact_id_convert_to_bigint is completed.
2. Define the index over job_artifact_id (index_geo_job_artifact_deleted_events_on_job_artifact_id) for the new job_artifact_id_convert_to_bigint column as well
3. Copy the FK
4. Swap columns

The implementation should follow that of !64577 (merged) (and the additional patch on !64973 (merged)).