✨ Enable structured authentication config flag

[cnvergence]

Summary

Enables flag for structured authentication flag that was planned as a follow-up during 1.30 k8s update.
I have added also an example guide to our dex guide made by MJ to verify the functionality.

Related issue(s)

Fixes #3216

Release Notes

Enable structured authentication configuration from a file with —authentication-config flag.

[kcp-ci-bot]

Hi @cnvergence. Thanks for your PR.

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[embik]

/ok-to-test

PR should have a release note since we're enabling a previously disabled flag.

[embik]

/retest

known issue.

[embik]

/approve

[kcp-ci-bot]

LGTM label has been added.

Git tree hash: 46a49184a86fbc77458b33f58e2357906da7f32e

[kcp-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: embik

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