Add fsgroupchangepolicy option

Please, answer some short questions which should help us to understand your problem / question better?

• Which image of the operator are you using? e.g. registry.opensource.zalan.do/acid/postgres-operator:v1.7.1
• registry.opensource.zalan.do/acid/postgres-operator:v1.7.0
• Where do you run it - cloud or metal? Kubernetes or OpenShift? [AWS K8s | GCP ... | Bare Metal K8s]
• Bare Metal K8s
• Are you running Postgres Operator in production? [yes | no]
• yes
• Type of issue? [Bug report, question, feature request, etc.]
• feature request

Would it be possible to add fsGroupChangePolicy option to the security context of created postgres statefulset?

Sometimes, kubelet changes access rights of data so that fsGroup GID can read/write data which postgres dislikes as security issue. This can be avoided by setting fsGroupChangePolicy: OnRootMismatch, so recursive chmod does not happen. This seems to be not possible currently so adding it as an option would be appreciated.

Locate the code that builds the created PostgreSQL StatefulSet and its pod security context, then trace how other StatefulSet options are configured. Add support for the requested fsGroupChangePolicy setting and check the existing operator tests or manifests for StatefulSet validation. Done means generated StatefulSets can use OnRootMismatch without changing unrelated security-context behavior.