allow skipping frontend build in Docker

That option allows having backend-only build,
skipping the long frontend build and test step.
Frontend developers run NodeJS locally and usually
don't need to have frontend built inside the docker image.

compose-dev-frontend.yml

@@ -13,6 +13,7 @@ services:
       dockerfile: Dockerfile
       args:
         - SKIP_BACKEND_TEST=true
+        - SKIP_FRONTEND_BUILD=true
         # - NODE_ENV=development
 
     image: umputun/remark42:dev