feat: add keycloak token exchange

[Cali0707]

This PR adds the code changes required to get the keycloak token exchange to work, as well as fixes the cluster keycloak config to work correctly

To use this you will need two openshift clusters, and then follow these steps:

1. Run make acm-install with your current context set to the cluster that will be your hub cluster
2. Run make keycloak-acm-setup-hub - this will take 20-30min as it needs to restart the api server
3. Create a kubeconfig that will connect to what will be your managed cluster
4. Run make keycloak-acm-register-managed-cluster CLUSTER_NAME=<your-choice-of-name> MANAGED_KUBECONFIG=<path-to-managed-kubeconfig>
5. Run make keycloak-acm-generate-toml
6. Run make build
7. Run ./kubernetes-mcp-server --port 8080 --config _output/acm-kubeconfig.toml

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Cali0707

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[openshift-merge-robot]

PR needs rebase.

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[openshift-ci]

@Cali0707: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/security	21547fd	link	false	/test security
ci/prow/images	21547fd	link	true	/test images
ci/prow/test	21547fd	link	true	/test test
ci/prow/fips-image-scan-openshift-mcp-server	21547fd	link	true	/test fips-image-scan-openshift-mcp-server
ci/prow/lint	21547fd	link	true	/test lint

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[Cali0707]

/hold

Will upstream as much as possible first, resync, then revisit this