[FR] Run appflowy on Heroku

**1~3 main use cases of the proposed feature**
It would be nice to have a setup to run appflowy on Heroku. I'm trying to do that by using the Docker image, but no luck. On the web exists tutorials about pushing rust and flutter to heroku, but not both together, but I'm sure that could be a way. I may try, but for the ones that know the codebase could be easier? :smiley:

**what types of users can benefit from using your proposed feature**
Everyone that want to give a try to AppFlowy.

**Additional context**
Add any other context or screenshots about the feature request here.