build: refactor production containers

Production containers now copy the Zeppelin source files at
build-time rather than using a shared volume. This means fewer
permission issues and backend/dashboard builds only have to run once
at build-time, not every time the containers are started.

Docs in PRODUCTION.md have been updated accordingly.

docker/production/backend/Dockerfile

@@ -0,0 +1,9 @@
+FROM node:18
+USER node
+
+COPY --chown=node:node . /zeppelin
+
+WORKDIR /zeppelin/backend
+RUN ls -lah
+RUN pwd
+RUN npm ci && npm run build