refactor: remove hardcoded namespaces from Kubernetes manifests

- Remove namespace: adopt-a-street from all metadata sections
- Update CouchDB NODENAME to use namespace-agnostic format
- Make all manifests deployable to any namespace
- Maintain service names and selectors for functionality
- All manifests validated with kubectl dry-run

Now manifests can be deployed to any namespace using:
kubectl apply -n <namespace> -f deploy/k8s/

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deploy/k8s/backend-deployment.yaml

@@ -2,7 +2,6 @@ apiVersion: v1
 kind: Service
 metadata:
   name: adopt-a-street-backend
-  namespace: adopt-a-street
   labels:
     app: backend
 spec:
@@ -19,7 +18,6 @@ apiVersion: apps/v1
 kind: Deployment
 metadata:
   name: adopt-a-street-backend
-  namespace: adopt-a-street
 spec:
   replicas: 2
   selector: