Enable Uvicorn reloading for local development

whythawk-full-stack-fastapi-postgresql#1
tiangolo/uvicorn-gunicorn-docker#1
tiangolo/uvicorn-gunicorn-docker#6

PR #1 updated the backend Docker image from
https://github.com/tiangolo/uvicorn-gunicorn-fastapi-docker
to https://github.com/br3ndonland/inboard (see https://inboard.bws.bio).
The previous Docker image had a start-reload.sh script, which started
Uvicorn with reloading. With inboard, there's no need for a separate
script. The same effect can be achieved with environment variables
(`PROCESS_MANAGER=uvicorn`, `WITH_RELOAD=true`).

Author: br3ndonland

backend.dockerfile

@@ -17,5 +17,7 @@ RUN bash -c "if [ $INSTALL_JUPYTER == 'true' ] ; then pip install jupyterlab ; f
 
 ARG BACKEND_APP_MODULE=app.main:app
 ARG BACKEND_PRE_START_PATH=/app/prestart.sh
-ENV APP_MODULE=${BACKEND_APP_MODULE} PRE_START_PATH=${BACKEND_PRE_START_PATH}
+ARG BACKEND_PROCESS_MANAGER=gunicorn
+ARG BACKEND_WITH_RELOAD=false
+ENV APP_MODULE=${BACKEND_APP_MODULE} PRE_START_PATH=${BACKEND_PRE_START_PATH} PROCESS_MANAGER=${BACKEND_PROCESS_MANAGER} WITH_RELOAD=${BACKEND_WITH_RELOAD}
 COPY ./app/ /app/