Enable VolumeSnapshotDataSource Feature Gate

[xing-yang]

What this PR does / why we need it:
This PR enables feature gate for VolumeSnapshotDataSource.

It also adds a condition called "DataPopulated" into PV. With the feature of snapshot and data source, volume might be created from snapshot source with data populated into the volume instead of an empty one. The external provisioner needs to understand the data source and also mark the condition "DataPopualted" to true. The PV controller will check this condition if the data source of PVC is specified. Only if the condition is true, the PVC can be marked as "Bound" phase.

Address design proposal: kubernetes/community#2495

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #
kubernetes/enhancements#177

Special notes for your reviewer:

Release note:

Allow volume to be created from a volume snapshot data source.

[neolit123]

@xing-yang is there a tracking issue for this API change?

[xing-yang]

@neolit123 Yes, it is here: kubernetes/enhancements#177

[neolit123]

@xing-yang
please link the issue in the first post so that others can see it and also add a Release note explaining the feature to the users reading the release notes for 1.12. 👍

thanks!

/kind feature

[neolit123]

/ok-to-test

[xing-yang]

@neolit123 Added a release note. Thanks!

[xing-yang]

/test pull-kubernetes-e2e-gce-100-performance

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: xing-yang
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[k8s-ci-robot]

@xing-yang: The following tests failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
pull-kubernetes-verify	795a2ba	link	/test pull-kubernetes-verify
pull-kubernetes-e2e-gce	795a2ba	link	/test pull-kubernetes-e2e-gce

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[xing-yang]

I've included changes in this PR to #67087. So this can be closed now.