Populate SourceVolumeMode in individual VolumeSnapshotContents

[xing-yang]

What happened:
There is a TODO here to Populate this field when volume mode conversion is enabled by default. Now that volume mode conversion is enabled by default, we should populate this field.
https://github.com/kubernetes-csi/external-snapshotter/blob/v7.0.0/pkg/sidecar-controller/groupsnapshot_helper.go#L448

What you expected to happen:

How to reproduce it:

Anything else we need to know?:

Environment:

• Driver version:
• Kubernetes version (use kubectl version):
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others:

[xing-yang]

/assign @RaunakShah

[Madhu-1]

@xing-yang Are you mentioned about prevent-volume-mode-conversion flag? if yes, it is only part of the snapshot-controller argument, as we don't have any flag in csi-snapshotter to check if the mode is enabled should we add a new flag to the csi-snapshotter as well?

[xing-yang]

@Madhu-1 I'm thinking we should probably get rid of this flag completely. @RaunakShah has brought this up. I need to double check on this.