fix(storage/kubernetes): only bracket IPv6 literals in in-cluster API host

[mridulgain]

Summary

• inClusterConfig() unconditionally wrapped KUBERNETES_SERVICE_HOST in [...]. Go's net/url only accepts brackets around a valid IPv6 literal, so any cluster with an IPv4 kubernetes Service ClusterIP (the common case) fails with invalid IP-literal and dex crash-loops on startup (cannot get kubernetes version).
• Extracted the bracketing logic into formatKubernetesHost(), which brackets only actual IPv6 literals.
• Found while verifying KAAP-2257 (fix(KAAP-2257): separate public redirect host from internal API host #77) against a QA image built with a newer Go toolchain, which tightened net/url validation and exposed this pre-existing bug (code unchanged since 2020).

Investigation

1. dex pod is clb

❯ k get po dex-test-du-ciprsmoke-5092765-7d557694dd-t787q  -n test-du-ciprsmoke-5092765
NAME                                             READY   STATUS             RESTARTS         AGE
dex-test-du-ciprsmoke-5092765-7d557694dd-t787q   0/1     CrashLoopBackOff   50 (4m11s ago)   3h55m

kubectl logs ... --previous revealed: invalid IP-literal parse error from failed to initialize storage: cannot get kubernetes version: parse "https://[10.96.0.1]:443/version"

Test plan

• go test ./storage/kubernetes/...
• Reproduced and confirmed the fix resolves url.Parse failure for an IPv4 host locally

QA verification

Built image: quay.io/platform9/pf9-dex:v2025.10.0-6-g19e9bf3f from this branch & patched the deploy,ment.

Result: pod came up clean, 1/1 Running, 0 restarts (vs. 50 restarts / CrashLoopBackOff before).

In the logs: (kubectl logs -n test-du-ciprsmoke-5092765 -l app.kubernetes.io/name=dex --tail=100)

1. Storage init succeeded (past the point where it previously crashed):

time=2026-09-02T12:06:13.569Z level=INFO msg="kubernetes client" api_version=dex.coreos.com/v1
time=2026-09-02T12:06:13.584Z level=INFO msg="creating custom Kubernetes resources"
...
time=2026-09-02T12:06:13.720Z level=INFO msg="config storage" storage_type=kubernetes

2. keystonefed-idp1 connector loaded:

time=2026-09-02T12:06:13.720Z level=INFO msg="config connector" connector_id=default
time=2026-09-02T12:06:13.720Z level=INFO msg="config connector" connector_id=keystonefed-idp1

3. Signing keys rotated:

time=2026-09-02T12:06:13.810Z level=INFO msg="keys expired, rotating"
time=2026-09-02T12:06:13.890Z level=INFO msg="keys rotated" next_rotation=2026-09-02T18:06:13.874Z

4. All servers listening:

time=2026-09-02T12:06:13.890Z level=INFO msg="listening on" server=telemetry address=0.0.0.0:5558
time=2026-09-02T12:06:13.890Z level=INFO msg="listening on" server=http address=0.0.0.0:5556
time=2026-09-02T12:06:13.891Z level=INFO msg="listening on" server=https address=0.0.0.0:5554
time=2026-09-02T12:06:13.891Z level=INFO msg="listening on" server=grpc address=0.0.0.0:5557