modify: support rollback

[huww98]

What type of PR is this?

/kind feature

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:

Support rollback to VAC A if modifying from A to B failed with a final error.
This works just like we modifying it again to C on final error.

The significant changes in the sync logic:

• Always retry if pvc.Status.ModifyVolumeStatus is not nil, which means the
  last transation does not finish successfully.
• Treat empty VAC name like refering to an special VAC with empty parameters,
  to support the use case of rolling back from non-nil VAC name to nil. We only
  allow this when no modify has been successfully applied, to avoid by-passing
  the quota system.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

The first 4 commits are already included in my other PRs. Please review the last commit. I will rebase when the previous PRs are merged.

Does this PR introduce a user-facing change?:

Support rolling back when modify failed

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: huww98
Once this PR has been reviewed and has the lgtm label, please assign msau42 for approval. For more information see the Code Review Process.

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[k8s-ci-robot]

Hi @huww98. Thanks for your PR.

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