Use distroless/static image for webhook

[WanzenBug]

What type of PR is this?
/kind cleanup

What bug does this PR fix?
Fixes #482

What this PR does / why we need it:

The webhook image needlessly used the distroless image containing glibc. The webhook server is a static binary, so it can be packaged using the distroless/static image like the other components.

This should make image security scanners happy. As minor benefits, it also slightly decreases image size and makes it so that the same base image is used for all components

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Changed the webhook image from distroless/base to distroless/static. 

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[k8s-ci-robot]

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[xing-yang]

/ok-to-test

[xinyanw409]

LGTM

[xing-yang]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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