create-app: update Dockerfile to set NODE_ENV=production

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/backend/Dockerfile

@@ -22,6 +22,9 @@ RUN apt-get update && \
 USER node
 WORKDIR /app
 
+# This switches many Node.js dependencies to production mode.
+ENV NODE_ENV production
+
 # Copy repo skeleton first, to avoid unnecessary docker cache invalidation.
 # The skeleton contains the package.json of each package in the monorepo,
 # and along with yarn.lock and the root package.json, that's enough to run yarn install.