Read oidc users namespace name from env

deployment.yaml

@@ -21,6 +21,8 @@ spec:
         - name: inventory-app
           image: inventory-app
           env:
+            - name: OIDC_USERS_NAMESPACE
+              value: "oidc-gateway"
             - name: INVENTORY_API_KEY
               value: "sptWL6XFxl4b8"
             - name: PYTHONUNBUFFERED