CLI: setup gitignore when checking out with git active (openfn project setup) #1576

The latest changes to openfn project mean we're going to start generating files which are not tracked by git (the checkout files per alias).

I think there are two things we need here:

• Create a setup utility which, if git is present, checks and updates the gitignore. This has flags and env vars which enable local state files to be checked in
• Before every checkout, run that setup to ensure the repo is in good working state. Again, add flags and env vars to disable setup-on-checkout

I think right now the only thing it has to do is update the gitignore file. Later it might have more responsibilities.