Implement upgrade procedure from older chart installations to newer installation using latest PostgreSQL chart
The chart switches to using a statefulset for PostgreSQL. The default behavior will be to use a new PV. Users will be required to perform a database backup (or
pg_dump) before upgrading, then reload the database with
pg_restore after the upgrade is complete. We should consider leveraging
templates/_checkConfig.tpl to help ensure that users don't inadvertently delete their databases. The default behavior on GKE at least could lead to this occurring.
The full set of steps needs to be implemented, verified, and documented.
This should be done after #1535 (closed), but included in the same release