Add replication lag check for all hosts in gcp

We should make this part of the procedure so that replication lag is checked on all hosts. Note that we also have this dashboarded in a few places.

• Triage - https://dashboards.gitlab.net
• postgres status - https://dashboards.gitlab.net/d/000000142/postgres-stats?orgId=1
• GCP failover - https://dashboards.gitlab.net/d/YoKVGxSmk/gcp-failover-gcp?orgId=1