Database Migration Playbook for Large PostgreSQL Cluster

Problem/Feature Description

A data engineering team needs to run a database schema migration across a fleet of postgres_servers. The migration script at /opt/migrations/run_migration.sh typically takes 15 to 45 minutes per server. When the team ran a previous migration synchronously, Ansible timed out and left servers in inconsistent states.

The team also needs to manage the pg_hba.conf access rules file using the community.postgresql collection (specifically community.postgresql.postgresql_pg_hba module) after the migration completes to add a new application user access rule.

The playbook must:

1. Launch the migration script asynchronously (fire and forget), then poll until it completes (max 1 hour).
2. After migration succeeds, use the community.postgresql collection to update pg_hba.conf with a new entry allowing app_user from 10.0.0.0/8 via md5 authentication.
3. Reload the PostgreSQL service if pg_hba.conf changes.

The servers run RHEL 9. Assume the necessary Python bindings are available.

Output Specification

Produce a complete Ansible playbook file named run_db_migration.yml. The playbook should include proper documentation of any collection dependencies.