Document new GH sync

[josephjclark]

Issue for comprehensive set of docs on the v2 sync and how to use it

Include a loom series:

• pulling projects
• deploying changes
• with github sync
• with sandboxes
• with multiple instances
• merge conflicts & divergence

[josephjclark]

One important thing to note with github sync and v2 project:

If you have a github v2 repo (you did openfn project pull) into it, and now you want to import that into the app, you have to create a config.json file with an { endpoint } key, and ignore warnings in the app UI. When pulling that GH into the app, the initial sync will work.

If you're pulling a project into an empty repo, and there's an empty openfn.yaml file in there, then it'll do a v2 sync and carry on with v2 from there (leaving a mostly redundant config.json file)