Change snapshot controller image version to 4.2.1

[smanjunath3]

What type of PR is this?

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:
This PR fixes issue 630. It changes the snapshot controller image version in the setup script to v4.2.1.
Which issue(s) this PR fixes:

Fixes #630

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

     NONE

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @smanjunath3. Thanks for your PR.

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[xing-yang]

Please also update the following images from 4.2.0 to 4.2.1:
https://github.com/kubernetes-csi/external-snapshotter/blob/release-4.2/deploy/kubernetes/csi-snapshotter/setup-csi-snapshotter.yaml#L87
https://github.com/kubernetes-csi/external-snapshotter/blob/release-4.2/deploy/kubernetes/webhook-example/webhook.yaml#L20

[xing-yang]

/ok-to-test

[xing-yang]

Can you squash your commits into 1?

[smanjunath3]

Can you squash your commits into 1?

done.

[xing-yang]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: smanjunath3, xing-yang

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