Remove PostgreSQL 11 from the Helm install

Summary

PostgreSQL 11 will no longer be supported in GitLab 14. The minimum required version will be PostgreSQL 12.

The chart today defaults to 11.10, however there are containers being built for 12 (12.5 at this time it seems): https://hub.docker.com/layers/bitnami/postgresql/12/images/sha256-35119659315dc09e0481cd7e83c4e7326b8ecd71bc67b85af3ecc2a313d9de9b?context=explore

Action

Remove PostgreSQL 11 from the Helm install.

Issue used when removing PG 10: #1985 (closed)