Add amcheck extension

What does this MR do?

This change adds a new PostgreSQL database extension called "amcheck" to the database initialization process. The amcheck extension provides functions for verifying the logical consistency of database structures, helping to detect potential corruption issues. This enhancement improves the database's ability to self-monitor and maintain data integrity alongside the existing text search and indexing extensions that were already being installed.

Omnibus MR: gitlab-org/omnibus-gitlab!8589 (merged)

Related issues

• See comment: gitlab-org/gitlab!198071 (comment 2644284316)

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