Documentation overhaul for patroni/postgres

During a recent failover production#637 (closed), we discovered a lot of old/outdated/missing information to cover our knowledge of patroni and it's control over postgres in our runbooks. Use this issue to sift through the following:

1. Go through our existing runbooks - remove anything that is out of date
2. Create new documentation covering aspects of configuration, troubleshooting, and operational tasks on the cluster
3. Create new documentation on restoration procedures per node and per cluster
4. Validate all postgres/patroni related alerts have appropriate runbooks
5. Add information on our use of On-Gres, and how we can page them for assistance