Bypass PgBouncer for auxiliary database connections
Performance wise, we are running into issues due to our polling-heavy design in Gitaly Cluster. Praefect must poll the (Cloud SQL) database frequently to determine if a repository is up to date. Ideally, this data should be pushed to Praefect asynchronously. Unfortunately, PgBouncer doesn't allow for this workflow (!2518 (comment 408074075)). To get around this, we may want to allow Praefect to bypass PgBouncer for auxiliary Cloud SQL database connections. An auxiliary database connection is one where a transient failure, such as during a Postgres restart/upgrade, doesn't prevent an RPC from succeeding. This way, we can continue using PgBouncer for essential connections, and permit auxiliary connections in cases where we can drastically improve performance.