Fix Heroku deploy script

[seadowg]

This updates the Heroku deploy script, so it works with the recent changes to Heroku's pricing plan (free tier add-ons are no longer supported). I've also fixed the custom buildpack/stack combo that was causing problems during deployment.

• I have reviewed the contributing guide

• I have made this pull request to the master branch

• I have run all the tests using ./test.sh.

• I have added the copyright headers to each new file added

• I have given myself credit in the humans.txt file (assuming I want to)

[seadowg]

It seems like ./test.sh is broken (on master). Running it in the dev docker image, I get:

rake aborted!
Errno::ENOSYS: Function not implemented - Failed to initialize inotify
/postfacto/api/config/environment.rb:35:in `<top (required)>'
/root/.rbenv/versions/2.7.3/bin/bundle:23:in `load'
/root/.rbenv/versions/2.7.3/bin/bundle:23:in `<main>'
Tasks: TOP => db:create => db:load_config => environment
(See full trace by running task with --trace)

[seadowg]

It seems like package.sh requires extra steps to create assets for TGZ deployment. I tried mimicking the steps that Github Actions performs, but it seems like that is no longer working (I run into problems at "Helm build").

I propose that we let packaging work without TGZ, until package.sh can perform can take care of it without extra steps.