feat(csi): allow setting annotation on StorageClass to determine VolumeSnapshotClass

[cfi2017]

This PR adds a way to specify the desired VolumeSnapshotClass by annotation in the StorageClass.

An example use case here is Nutanix: The Nutanix CSI driver uses a single provisioner but allows for StorageClasses on either NFS (NutanixFiles) or Volumes (NutanixVolumes). These two StorageClasses require differently configured VolumeSnapshotClasses even though they use the same provisioner.

In Velero, currently, this is only supported by setting an annotation on every PVC you want to back up.

A more scalable approach is to allow setting a default for the StorageClass.

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file (make new-changelog) or comment /kind changelog-not-required on this PR.
• Updated the corresponding documentation in site/content/docs/main.

[cfi2017]

For reference, this is the same PR I first opened in the old CSI plugin repo, before realising that repo is outdated.

vmware-tanzu/velero-plugin-for-csi#237

[codecov]

Codecov Report

Attention: Patch coverage is 70.83333% with 7 lines in your changes missing coverage. Please review.

Project coverage is 59.39%. Comparing base (a9031eb) to head (218f588).
Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/util/csi/volume_snapshot.go	69.56%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8646   +/-   ##
=======================================
  Coverage   59.39%   59.39%           
=======================================
  Files         370      370           
  Lines       39952    40009   +57     
=======================================
+ Hits        23730    23765   +35     
- Misses      14731    14750   +19     
- Partials     1491     1494    +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[cfi2017]

@kaovilai is code coverage for error logs something that's needed for approval?