feat: add migration to set the pgAudit config

[patheard]

Summary

Add migration to disable pgAudit on the app_db_user and rdsproxyadmin roles. This is being done to save costs and reduce the logging pressure on the database instances.

Related Issues | Cartes liées

• https://github.com/cds-snc/platform-core-services/issues/508

Test instructions | Instructions pour tester la modification

Check that no add_db_user or rdsproxyadmin queries are logged by pgAudit.

Release Instructions | Instructions pour le déploiement

This will fail if the target database does not have pgAudit enabled.

Reviewer checklist | Liste de vérification du réviseur

• [ ] This PR does not break existing functionality.
• [ ] This PR does not violate GCNotify's privacy policies.
• [ ] This PR does not raise new security concerns. Refer to our GC Notify Risk Register document on our Google drive.
• [ ] This PR does not significantly alter performance.
• [ ] Additional required documentation resulting of these changes is covered (such as the README, setup instructions, a related ADR or the technical documentation).

⚠ If boxes cannot be checked off before merging the PR, they should be moved to the "Release Instructions" section with appropriate steps required to verify before release. For example, changes to celery code may require tests on staging to verify that performance has not been affected.