[Service Monitor] Support multiple namespaces per Helm release

• Change DiagnosisRequest.NameSpace (string) to ServiceNamespaces ([]string) and update validation rules.

• Pass namespace list over Kafka headers: JSON-encode namespace lists into headers in buildKubeConfigRequestHeaders and resumeStateFromHeaders.

• Update kubeconfigResumeState, sessions.New(), and Session to store namespace slices ([]string).

• Create one dynamic informer factory per namespace and merge events into the main debounce channel.

• Query resources per namespace per GVR in assessRelease and aggregate results before calling AggregateHealth. Align StopRequest: Rename StopRequest.NameSpace to ServiceNamespaces for consistency.