feat(REPL): poc for heroku REPL and prompt mode

[justinwilaby]

This PR provides the POC for both Heroku REPL and Heroku "Prompt" modes

Usage:

REPL mode

heroku with no command or ./bin/run with no args, flags or commands.
-- Type commands as per usual

Prompt Mode

use the --prompt flag. e.g. heroku apps:create --prompt
-- The cli will ask you for all inputs starting with required flags and args then optional

[ekozilforce]

This looks really 🔥 . I like how this takes advantage of oclif metadata to deliver value without plugin development overhead.

I'm interested in learning how we can iterate on this to allow flexibility for plugin developers to provide their own prompt behavior. If this project goes down that path, I'd love to be an internal tester using our data plugins. 🤙 when the time comes