Introduce the four-step PatternFly wizard (Clusters, Configure, Policy,
Review) without Submariner or Globalnet pre-pair validation yet.

Watch ManagedClusterAddOn health for the selected cluster pair, gate the
Configure step on canProceed, and keep evaluation in mco utils/hooks.

How Submariner is checked (ACM path):
- Hub watch only: ManagedClusterAddOn named "submariner" per managed
  cluster namespace (RHACM Networking docs). No ManagedClusterView in
  this PR; spoke Broker/Cluster CRs are for upstream/Globalnet later.
- NotInstalled: addon object missing (usual) or watch 404 (absent API
  resource) — not a condition on the MCA spec. Both missing => skip
  validation and allow Next (UX: Cluster network - Skipped).
- Per cluster after addon exists: Available first
  (SubmarinerAgentAvailable=True); then connected
  (SubmarinerConnectionDegraded=False) => Healthy. ConnectionDegraded,
  AgentDegraded, RouteAgentConnectionDegraded, or unlabeled gateway =>
  Degraded. Available not ready / connection unset => Progressing.
- Pair gate: both NotInstalled or both Healthy => canProceed; one-sided
  install => Inconsistent (block); otherwise Degraded/Progressing block.

Why this combination (vs connectivity-only):
- Available then ConnectionDegraded matches ACM's documented MCA
  conditions for deploy + established connections. Extra degraded
  signals (agent/route/gateway) fail closed so we do not treat a
  half-ready addon as connected. Can narrow the gate later if product
  wants ConnectionDegraded alone.

Out of scope here: Globalnet/CIDR overlap warnings, MCV lifecycle.