Add default podSecurityContext to fix /data volume permissions

[arteonprifti]

Adding podSecurityContext should fix the permissions for the volume:
https://kubernetes.io/docs/tasks/configure-pod-container/security-context/#set-the-security-context-for-a-pod

[nscuro]

Thanks for the PR @arteonprifti!

Unfortunately, this won't work with OpenShift. So it's probably best to wrap the securityContext in an if or with template block to highlight it being optional.

Perhaps also add a comment in values.yaml that points out that it will need to be set to null explicitly for OpenShift.

[arteonprifti]

@nscuro updated as required

[nscuro]

Marking as breaking change because OpenShift users will need to explicitly unset the new value.