Include a list of apt package names to be installed in a file named Aptfile

[dbeatty10]

Description

Resolves #334

Commands

The first and last commands below are only to show which buildpacks have been installed. It's really only the middle command that adds the necessary buildpack:

heroku buildpacks --app dbt-hubcap
heroku buildpacks:add --index 1 heroku-community/apt --app dbt-hubcap
heroku buildpacks --app dbt-hubcap

Afterwards, the app needs to be re-deployed per these instructions.