* feat: add --cluster-domain flag for custom cluster domains
Kubernetes clusters can use a custom domain via --cluster-domain
(kubelet) instead of the default cluster.local. The controller
hardcoded cluster.local when constructing backend service FQDNs,
causing DNS resolution failures on clusters with custom domains.
Add a --cluster-domain flag (default: cluster.local) and expose
it as a Helm value (clusterDomain).
Fixes #263
* test: use custom cluster domain in tests to verify --cluster-domain flag
Use non-default cluster domains across unit, integration, and e2e tests
to ensure the clusterDomain parameter is actually propagated rather than
relying on the default "cluster.local". Also enrich descriptions for the
--cluster-domain flag and the Helm clusterDomain value.
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Co-authored-by: Zhiqiang ZHOU <im@strrl.dev>