Add GetGroupControllerCapabilities common function

[carlory]

What type of PR is this?

/kind feature

What this PR does / why we need it:

external-volumesnapshot want to use it to check group controller caps

Does this PR introduce a user-facing change?:

Add GetGroupControllerCapabilities common function

[carlory]

/hold

It's blocked by #132

[xing-yang]

Can you add a unit test?

[carlory]

/hold cancel

Can you add a unit test?

@xing-yang added.

[xing-yang]

/lgtm
/approve

[k8s-ci-robot]

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This pull-request has been approved by: carlory, xing-yang

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[carlory]

Hi @xing-yang , may I ask where I can see the version release cycle of this repo?

because I want to use the new func GetGroupControllerCapabilities to check group controller caps in external-snapshotter.

https://github.com/kubernetes-csi/external-snapshotter/blob/master/cmd/csi-snapshotter/main.go#L231