[Breaking] Bump postgres chart to latest release (#391)

See discussion in #387

Upgrade notes to Chart v11.x and Postgres 14.x: https://docs.bitnami.com/kubernetes/infrastructure/postgresql/administration/upgrade/

The current version in Gitea is using `11.11.0-debian-10-r62` from 2021-04.

Bumping the chart to the latest (v12.x) would use the image `15.2.0-debian-11-r14` which would be a jump from postgres 11 to postgres 15. There are no specific notes for the v12.x chart release, hence we might be able to just go to 12.x directly.

There have been some param renamings which I've reflected in the README.

**⚠️ BREAKING**

Users have to migrate their Postgres DB by e.g. restoring a previously created database dump into a clean installation.

Co-authored-by: justusbunsi <sk.bunsenbrenner@gmail.com>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/391
Reviewed-by: techknowlogick <techknowlogick@noreply.gitea.io>
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.io>
Co-authored-by: pat-s <patrick.schratz@gmail.com>
Co-committed-by: pat-s <patrick.schratz@gmail.com>

Chart.lock

@@ -6,10 +6,10 @@ dependencies:
   repository: https://raw.githubusercontent.com/bitnami/charts/pre-2022/bitnami
   version: 6.14.10
 - name: postgresql
-  repository: https://raw.githubusercontent.com/bitnami/charts/pre-2022/bitnami
-  version: 10.3.17
+  repository: oci://registry-1.docker.io/bitnamicharts
+  version: 12.2.6
 - name: mariadb
   repository: https://raw.githubusercontent.com/bitnami/charts/pre-2022/bitnami
   version: 9.3.6
-digest: sha256:eb786e862718ddd8c66d66b0a7d3501bd7fbb3c8edef12a406c9544159971965
-generated: "2023-02-26T13:51:59.1429398+01:00"
+digest: sha256:2115873999bfccaaa3308dd4cd374def696572938cc240079ea338b9d8fd9723
+generated: "2023-03-27T10:04:33.619453+02:00"