Update Patroni/Postgres replica creation runbooks to reflect recent changes.

Current Situation

Recent fixes and changes to our Chef cookbooks have made https://gitlab.com/gitlab-com/runbooks/-/blob/master/docs/patroni/patroni-management.md to be incorrect in describing how to add replicas to the Patroni cluster.

via https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/13324#status

• We have decoupled the locations of postgres_config_dir and pguser_home_dir
  • gitlab-cookbooks/gitlab-patroni!82 (merged)
  • gitlab-cookbooks/gitlab-patroni!85 (merged)
  • gitlab-cookbooks/gitlab-patroni!86 (merged)
• However, Chef generates postgres.base.conf and postgres.conf, and various cookbooks expect this to be case
  • The scope of changes is amplified significantly, so updating those cookbooks is unwise at the moment
  • Thus, we want to reach a point where a baseline replica is provisioned that requires minimal manual intervention after provisioning
    • We have to delete the chef-provisioned configuration files and let Patroni regenerate them
    • We need to create a runbook to capture this(https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/13343)

Desired Outcome

• Make necessary changes the https://gitlab.com/gitlab-com/runbooks/-/blob/master/docs/patroni/patroni-management.md and any associated runbooks in order to reflect the new process of adding a replica: gitlab-com/runbooks!3568 (merged)