Convert deployments columns to bigint

Summary

Track the bigint conversion of deployments separately from related tables.

This work belongs to &20032.

The conversion covered these columns in two phases:

• Phase one: id and environment_id
• Phase two: project_id and user_id

Completed work

• Initialize the bigint conversion and backfill existing rows in !194972 (merged).
• Complete the phase-one swap and temporary object cleanup in !221371 (merged).
• Complete the phase-two swap in !248015 (merged).
• Remove the phase-two temporary indexes and foreign key in !248030 (merged).

Follow-up work

• Remove the old integer shadow columns and synchronization trigger in #551605 (closed).
• Remove the Deployment ignore rules one release later in #551606 (closed).

deployment_clusters and deployment_merge_requests follow separate release timelines and are tracked in their own parent work items.