Add CA rotation TM test

[dimitar-kostadinov]

How to categorize this PR?

/area testing
/kind test

What this PR does / why we need it:
Add certificate rotation Test Machinery test to verify that registry cache is working after the Prepared and Completed rotation phases.

Which issue(s) this PR fixes:
Part of #203

Special notes for your reviewer:
The PR will be draft until #245 is merged.

Release note:

A new TM test to verify that registry cache is working after CA rotation is now added.

[gardener-prow]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[gardener-ci-robot]

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• After 15d of inactivity, lifecycle/stale is applied
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You can:

• Mark this PR as fresh with /remove-lifecycle stale
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/lifecycle stale

[dimitar-kostadinov]

/remove-lifecycle stale

[gardener-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ialidzhikov]

/assign