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.
• Keep reconciling to the previous target if spec is rolled back to nil, until
  it succeeds or we get an infeasible error. Then we just leave it at its
  current state and stop reconciling for it, since user may not care about it
  now.

See kubernetes/enhancements#5482 for details

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

The first 2 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
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[k8s-ci-robot]

Hi @huww98. Thanks for your PR.

I'm waiting for a kubernetes-csi member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[huww98]

Implementation of kubernetes/enhancements#5482