Use CMD alongside ENTRYPOINT in the Dockerfile (#3366)

This allows for runtime customization, see #3362.

docker/Dockerfile

@@ -28,3 +28,4 @@ ARG COMMIT
 RUN echo "{\"hash\": \"$COMMIT\"}" > .hash.json
 
 ENTRYPOINT ["./run.sh"]
+CMD ["npm", "start"]

docker/run.sh

@@ -13,4 +13,4 @@ if [ ! -f "$DATA/configuration.yaml" ]; then
     cp /app/configuration.yaml "$DATA/configuration.yaml"
 fi
 
-exec npm start
+exec "$@"