Helm Chart: Openshift SecurityContextConstraints

The helm chart currently detects if Minio is being deployed on OpenShift and deploys an additional `SecurityContextConstraints` resource if it is. This requires admin privileges beyond what you would expect a typical developer / OpenShift project admin to have. Maybe someone with more history can explain the original thinking here, but it seems that we are adding a new `SecurityContextConstraints` to OpenShift that allows Minio to run with a more relaxed `SecurityContext` when we could instead just deploy Minio with a tighter `SecurityContext` that conforms to standard / existing ones. We are able to run Minio without `allowPrivilegeEscalation` and with random UIDs/fsGroup that OpenShift requires (but perhaps there are some features that require this that I am not aware of.)