Add VolumeGroupSnaphot examples

[leonardoce]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

This PR adds two examples of how a VolumeGroupSnapshotClass and a VolumeGroupSnapshot can be defined.
The examples use the CSI Hostpath Driver.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

NONE

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

Hi @leonardoce. Thanks for your PR.

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[nixpanic]

This is nice to have, will make it much easier for others to try it out, thanks!

/lgtm

[nixpanic]

/ok-to-test

[nixpanic]

/assign xing-yang

[xing-yang]

Can you please add a comment here that the PVC will need to have this label for it to be included in the VolumeGroupSnapshot?

[xing-yang]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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