Add support for Kubernetes Pod Security Policy

**Is your feature request related to a problem?/Why is this needed**
We run secure Kubernetes 1.16+ environments where Pod Security Policies (PSP) is required for any Pod to start. When we deploy the helm package for the SMB FlexVolume plugin it fails to start

**Describe the solution you'd like in detail**
The helm package includes PSP support, including creating the service account under which the installer pod runs as.

**Describe alternatives you've considered**
Manually create the required Kubernetes definitions to support PSP, including post-installation change to the installer's deployment - however it's more effective to have that supported out of the box.

**Additional context**
See https://kubernetes.io/docs/concepts/policy/pod-security-policy/

Start by locating the Helm package and the installer's deployment and service-account definitions. Read the Kubernetes Pod Security Policy documentation linked in the issue, then compare the package's current resources with the requirements for a PSP-enabled cluster. Done means the SMB FlexVolume plugin can be deployed in a Kubernetes 1.16+ environment where PSP is required, without manual resource or deployment changes.

Written by the indexing model from the issue text.