Please add the amcheck extension to the whitelist of supported PostgreSQL extensions.

Use case:

- GitLab requires amcheck for database integrity verification

- amcheck provides functions to verify the logical consistency of B-Tree indexes

- It's a core PostgreSQL contrib module (not third-party)

- Essential for detecting index corruption before it causes data loss

Current status:

- Extension exists in pg_available_extensions but cannot be installed

- Error: permission denied to create extension "amcheck" / Must be superuser

- Not included in extwlist.extensions

Impact:

- Blocks GitLab migrations to DO Managed PostgreSQL

- Limits database health monitoring capabilities

Reference:

- https://www.postgresql.org/docs/current/amcheck.html

- https://docs.gitlab.com/install/postgresql_extensions/