Docs feedback: Missing step for PgBouncer while upgrade postgres

https://docs.gitlab.com/ee/administration/postgresql/replication_and_failover.html#upgrading-postgresql-major-version-in-a-patroni-cluster

There is a step missing in the linked upgrade guide. Restarting PgBouncer should be noted as a step, otherwise GitLab won't get the information about the new postgres server version and the information in the admin panel will be wrong.