Allow runs without HEROKU_API_KEY when no app is being deployed

[schneems]

Right now if you Heroku::Runner.new() it will look for a HEROKU_API_KEY or shell out to heroku token even if you never plan on deploying.

====>> Hatchet setup
  #!/bin/bash -eo pipefail
bundle exec hatchet ci:setup

Traceback (most recent call last):
	3: from /home/circleci/project/vendor/bundle/ruby/2.7.0/gems/heroku_hatchet-7.3.3/etc/ci_setup.rb:16:in `<main>'
	2: from /home/circleci/project/vendor/bundle/ruby/2.7.0/gems/heroku_hatchet-7.3.3/etc/ci_setup.rb:16:in `open'
	1: from /home/circleci/project/vendor/bundle/ruby/2.7.0/gems/heroku_hatchet-7.3.3/etc/ci_setup.rb:19:in `block in <main>'
/home/circleci/project/vendor/bundle/ruby/2.7.0/gems/heroku_hatchet-7.3.3/etc/ci_setup.rb:19:in `fetch': key not found: "HEROKU_API_USER" (KeyError)
bundler: failed to load command: hatchet (/home/circleci/project/vendor/bundle/ruby/2.7.0/bin/hatchet)
RuntimeError: Command /home/circleci/project/vendor/bundle/ruby/2.7.0/gems/heroku_hatchet-7.3.3/etc/ci_setup.rb failed:
== Setting Up CI ==

This is an issue for people who are using hatchet locally and never need to deploy (if they're using in_directory_fork for example).

The issue is that the reaper needs the API token, and the reaper is created in the initialize method.

Ideas to fix:

• Introduce a Hatchet::Local that only has a very limited set of hatchet features and does not depend on the reaper
• Refactor the reaper relationship in App to be lazilly initialized when it's called.