[release/v2.21] Include tunneling agent IP in apiserver's TLS cert SAN

[rastislavs]

What this PR does / why we need it:

This is a manual backport of #11932

Which issue(s) this PR fixes:

Fixes #11930

What type of PR is this?
/kind bug

Special notes for your reviewer:

Does this PR introduce a user-facing change? Then add your Release Note here:

Include tunneling agent IP in apiserver's TLS cert SANs

Documentation:

NONE

[embik]

/approve

[kubermatic-bot]

LGTM label has been added.

Git tree hash: 760c9195f531505b01bfc22cb7c21afaed33b70f

[kubermatic-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: embik, rastislavs

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• pkg/controller/OWNERS [embik]
• pkg/resources/OWNERS [embik]

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[rastislavs]

/cherrypick release/v2.20

[kubermatic-bot]

@rastislavs: #11933 failed to apply on top of branch "release/v2.20":

Applying: Include tunneling agent IP in apiserver's TLS cert SAN
Using index info to reconstruct a base tree...
M	pkg/controller/seed-controller-manager/kubernetes/resources.go
M	pkg/resources/apiserver/tls-serving-certificate.go
M	pkg/resources/data.go
Falling back to patching base and 3-way merge...
Auto-merging pkg/resources/data.go
CONFLICT (content): Merge conflict in pkg/resources/data.go
Auto-merging pkg/resources/apiserver/tls-serving-certificate.go
Auto-merging pkg/controller/seed-controller-manager/kubernetes/resources.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Include tunneling agent IP in apiserver's TLS cert SAN
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherrypick release/v2.20

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