add redpanda to legion cluster

Deploy single-broker Redpanda in dedicated namespace with 20Gi storage,
1 CPU / 2Gi memory limits, and a one-shot topic init job for neuron.swarm,
neuron.ci, neuron.vcs, and neuron.webhooks with appropriate retention.

servers/legion/apps/redpanda.yaml

@@ -11,7 +11,7 @@ spec:
     path: servers/legion/k8s/redpanda
   destination:
     server: https://kubernetes.default.svc
-    namespace: platform
+    namespace: redpanda
   syncPolicy:
     automated:
       prune: true