deploy neuron marketing site to neurontechnologies.ai

Add marketing/ manifests (Deployment, Service, ExternalSecret) for the
Next.js marketing site in neuron-prod namespace, an Argo CD app pointing
to the new path, and update the prod ingress to serve / from neuron-marketing
instead of neuron-rest.

servers/legion/apps/neuron-marketing.yaml

@@ -0,0 +1,20 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: neuron-marketing
+  namespace: argocd
+spec:
+  project: default
+  source:
+    repoURL: http://10.43.1.53:3000/will/infrastructure.git
+    targetRevision: main
+    path: servers/legion/k8s/neuron-technologies/marketing
+  destination:
+    server: https://kubernetes.default.svc
+    namespace: neuron-prod
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true
+    syncOptions:
+      - CreateNamespace=false