Update the default postgresql to PG 13 or 14

Summary

In GitLab 16.0, support for Postgres 12 is being dropped, and support for PG 14 is intended to be added.

In the the GitLab 15.11 milestone we should

• complete an investigation and POC of updating our bitnami postgres chart to the newest version
• Investigate whether our chart DB upgrade steps are viable for jumping from pg12 to 14 (doing a two version jump allows us to only force our users to do this every two years in charts for those using the provided database)

In the Gitab 16.0 milestone we need to:

• Update the PG min-version checks to PG 13
• Set the default postgres image version to 14 (or 13 if 14 isn't feasible)
• Update the bitnami postgres chart if feasible
• Ensure all the db upgrade documentation is up to date and accurate for the chart