feat(monitoring) pg xid wraparound resource saturation monitoring

Closes gitlab-com/gl-infra/infrastructure#9965

Postgres Wraparound Saturation Monitoring

This change adds saturation monitoring for Postgres TXIDs.

Crunchydata wrote an excellent blog post about this: https://blog.crunchydata.com/blog/managing-transaction-id-wraparound-in-postgresql

This relies on metrics from gitlab-cookbooks/gitlab-exporters!224 (merged). Not that with chef-client being disabled in production, these metrics are currently only being collected in staging. Once chef-client is re-enabled in staging, the required metrics will be collected for production too.

https://dashboards.gitlab.net/dashboard/snapshot/n3J1lNUJBD5qlas4soOEnxj5bTdKM25a?orgId=1&var-PROMETHEUS_DS=Global&var-environment=gstg&var-type=patroni&var-stage=main&from=now-24h&to=now