feature: support for structured authentication config

[embik]

Feature Description

Kubernetes supports an authentication config file since Kubernetes 1.30. I disabled the --authentication-config flag in the 1.30 rebase, but it would be nice to be able to harness the advanced configuration capabilities of this file in kcp as well.

Proposed Solution

Enable --authentication-config flag and wire it up into the generic controlplane coming from Kubernetes.

Alternative Solutions

No response

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• I would like to work on this issue.

Additional Context

No response

[xmudrii]

I'd like to take this issue, I already started investigating.
/assign