run live_debug if feature spec fails locally

Stacktraces and screenshots are complicated, so I prefer interactive debug. live_debug is really convenient, but having to:

1. run tests
2. parse failures from big red stacktrace
3. manually add some live_debugs as needed
4. rerun tests
5. repeat from 1.
6. push fix
7. remove some forgotten live_debugs

We could eliminate steps 2-7 if there was a flag to pause on failures, that automatically ran live_debug. e.g. rspec spec/feature/some_spec.rb --debug-errors

Byebug or capybara can probably do something like this, but I am not sure how.

Another example: https://github.com/conradirwin/pry-rescue