Document feature-gates and their compatibility

[omniproc]

A feature-gate compatibility matrix would be great so it is clear which feature-gate can be used in which situation and what the feature-gate will do. Some feature gates can not be together. Some can only be used with a specific vSphere or Kubernetes version. Some are only supported with a specific CSI flavor (supervisor / Tanzu only). Currently it is nearly impossible for a user to find out what is supported and what not. Many feature gates lack even basic documentation of what they will actually do.

[divyenpatel]

@omniproc we do not expect any feature gate change in the published yaml. we are adding feature gates only for development and release purpose.

if fss is enabled in the released yaml shipped with tag, do not change fss value.

from https://github.com/kubernetes-sigs/vsphere-csi-driver/releases/tag/v3.2.0 we can not disable GAed feature gates using internal fss configmap.

for Alpha features we will make sure to publish doc here - https://github.com/kubernetes-sigs/vsphere-csi-driver/tree/master/docs/book/features