Forward to a new hosting provider while migrating off of Heroku.
Original motivation: awseward/call_status#171
heroku create
heroku config:set FWD_TO='https://your-app.example.com'
heroku stack:set container
git push heroku main
docker build -t hk-proxy .
docker run -it --rm \
-p 5000:81 \
-e PORT=81 \
-e FWD_TO='https://your-app.example.com' \
--name web \
hk-proxy