Automate k8s Postgresql Upgrades after 3.0.0 release

[artntek]

(discussed with @mbjones in ESS-DIVE Meeting)

We will release the 3.0.0 metacat helm chart with postgres v14 as a subchart.

The Metacat helm chart appears to work ok with postgres 14, 15, 16, when starting up with a new database.

However, upgrading between these major versions currently requires manual intervention.

It is up to individual operators to ensure the mounted data directory has been manually upgraded to be compatible with postgresql v14 before installing the helm chart.

After the v3.0.0 release, however, we will find a way to automate postgres upgrades (but only from the previous version to the new version), so that if operators stay up to date with metacat releases, their upgrades should be seamless

Some examples of container-specific solutions:

• https://stackoverflow.com/questions/64850625/how-to-upgrade-postgresql-inside-a-kubernetes-pod
• Upgrading between major versions? docker-library/postgres#37 (comment)
• https://hub.docker.com/r/tianon/postgres-upgrade/

Official postgres documentation; see in particular:

• 19.6.2. Upgrading Data via pg_upgrade
• 19.6.3. Upgrading Data via Replication