Enable remote debugging with ptvsd (#3419)

* open port 3000 for remote debugging

* add ptvsd

* use port 5678 to avoid changes in VSCode's default config

* attach to ptvsd

* no need to wait for attach

* actually, --debugger seems to be working

* create a new docker entry point for remote debugging

* alternative method to switch to debugging

bin/docker-entrypoint

@@ -39,6 +39,7 @@ help() {
   echo ""
   echo "shell -- open shell"
   echo "dev_server -- start Flask development server with debugger and auto reload"
+  echo "debug -- start Flask development server with remote debugger via ptvsd"
   echo "create_db -- create database tables"
   echo "manage -- CLI to manage redash"
   echo "tests -- run tests"
@@ -72,6 +73,11 @@ case "$1" in
     export FLASK_DEBUG=1
     exec /app/manage.py runserver --debugger --reload -h 0.0.0.0
     ;;
+  debug)
+    export FLASK_DEBUG=1
+    export REMOTE_DEBUG=1
+    exec /app/manage.py runserver --debugger --no-reload -h 0.0.0.0
+    ;;
   shell)
     exec /app/manage.py shell
     ;;