Support extra Heroku apps:create options - region, space, team

[annapowellsmith]

It would be useful to document how to pass Heroku CLI options on datasette publish, e.g. --region eu.

[simonw]

It looks like there are a few extra options we should support:

https://devcenter.heroku.com/articles/heroku-cli-commands

  -t, --team=team            team to use
  --region=region            specify region for the app to run in
  --space=space              the private space to create the app in

Since these differ from the options for Zeit Now I think this means splitting up datasette publish now and datasette publish Heroku into separate subcommands.

[simonw]

Now that I've split the heroku command out into a separate default plugin this is a much easier thing to add: https://github.com/simonw/datasette/blob/master/datasette/publish/heroku.py