deploy(nxtgauge-backend): centralize image tag and align gateway port

apps/nxtgauge-backend/base/configmap.yaml

@@ -6,3 +6,4 @@ metadata:
 data:
   NODE_ENV: "production"
   PORT: "2002"
+  GATEWAY_PORT: "2002"

apps/nxtgauge-backend/base/deployment.yaml

@@ -17,7 +17,7 @@ spec:
     spec:
       containers:
         - name: backend
-          image: ghcr.io/traceworks2023/nxtgauge-backend:latest
+          image: ghcr.io/traceworks2023/nxtgauge-backend
           imagePullPolicy: IfNotPresent
           ports:
             - containerPort: 2002

apps/nxtgauge-backend/overlays/prod/kustomization.yaml

@@ -4,3 +4,6 @@ resources:
   - ../../base
 patchesStrategicMerge:
   - replicas-patch.yaml
+images:
+  - name: ghcr.io/traceworks2023/nxtgauge-backend
+    newTag: latest