Add examples of useful GitHub Actions for theme development

[bookernath]

What?

Add a few examples of useful GitHub actions for theme development.

1. Automatically deploy theme to a production store on merge to master/main
2. As a scheduled job, check for changes to the production store's configuration and create a PR back to the repo to keep things in sync

[bigbot]

Autotagging @bigcommerce/storefront-team @davidchin

[junedkazi]

Do we want to add a readme file as well in this repo to call out how to use it and how to setup some of these secrets ?

[bookernath]

I plan to get some public dev docs posted... can do another PR to add a link once we have those