add postgres securityContext at pod level

[dstraub]

SUMMARY

The description for postgres_security_context_settings '...will be set under the pod-level securityContext field' is wrong, this settings are injected in container-level securityContext.
For setting on pod-level the field postgres_pod_security_context_settings is added

ISSUE TYPE

• Bug

ADDITIONAL INFORMATION

For some CSI-Drivers (e.g. Longhorn) it's required to modify the securityContext on pod-level.
(see also https://longhorn.io/docs/1.7.0/nodes-and-volumes/volumes/pvc-ownership-and-permission).

The existing field postgres_security_context_settings is for container-level.
Maybe this field should renamed to postgres_container_security_context_settings.

    ...
        volumeMounts:
        - mountPath: /var/lib/pgsql/data
          name: postgres-15
          subPath: data
      dnsPolicy: ClusterFirst
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext:
        fsGroup: 26
        fsGroupChangePolicy: Always
      terminationGracePeriodSeconds: 30
    ...