add --home and --shell to rails user in Dockerfile (rails#47533)

Author: rubys

railties/lib/rails/generators/rails/app/templates/Dockerfile.tt

@@ -73,7 +73,7 @@ RUN apt-get update -qq && \
     rm -rf /var/lib/apt/lists /var/cache/apt/archives
 
 # Run and own the application files as a non-root user for security
-RUN useradd rails
+RUN useradd rails --home /rails --shell /bin/bash
 USER rails:rails
 
 # Copy built artifacts: gems, application