Disable setting features in PVC definition

[acsulli]

Currently, storage features such as snapshot policy, export policy, etc. can be configured with a default in the backend definition, but that can be overridden at any time in the PVC. Sometimes it's desirable to prevent the PVC from overriding specific settings for several reasons: security, supportability, control.

Having the ability to disable, or provide a predefined set of approved values, for settings which can be manipulated via the PVC definition would help to alleviate those concerns.

Andrew