Update doc and code regarding restic

[xing-yang]

Describe the bug
In the upcoming Velero v1.10 along with the introduction to support kopia, some of the CLI parameters, resources are renamed:
Design doc: https://github.com/vmware-tanzu/velero/blob/main/design/unified-repo-and-kopia-integration/unified-repo-and-kopia-integration.md

More details in the code change:
vmware-tanzu/velero#5370
vmware-tanzu/velero#5390
vmware-tanzu/velero#5432

We need to update the following doc section and test it:
https://github.com/vmware-tanzu/velero-plugin-for-vsphere/blob/main/docs/vanilla.md#backup-vsphere-cns-file-volumes

Command to install Velero with restic is changed:
https://github.com/vmware-tanzu/velero/blob/main/design/unified-repo-and-kopia-integration/unified-repo-and-kopia-integration.md#installation

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[xing-yang]

There are additional changes needed in vSphere plugin code. These changes are not Must Have, but they make plugin code consistent with the new Velero code:

• Replace the call of restic.GetPodVolumesUsingRestic with podvolume.GetVolumesByPod. If this is not changed in plugin code, plugin has to refer to the old Velero code all the time, because in Velero 1.10, the function restic.GetPodVolumesUsingRestic has been deleted.
• Remove the irrational appearance of “restic” word in plugin code/comments/logs.

Refer to this PR as an example of the aforementioned changes 1 and 2.