Add GraphQL Auth plugin and configure user groups

[kylepratuch]

@dananjohnson I'm leaving this as a draft until we're sure the plugin/groups are configured correctly for the client side of things.

[kylepratuch]

This branch contains the Craft updates needed to support @dananjohnson's work implementing authentication in the client. If you're familiar with the setup we used on the main site, there's really nothing new here.

I do want to note a few things (some of which we discussed on a call earlier today):

• If you're testing this with the locally stored db dump, there's a chance the Educator and Student user group ids won't match the project config. The mismatch manifests as user groups being assigned the wrong schema in the GQL auth plugin settings. With a persistent database this shouldn't happen, but if you see it in a dev environment you can ask Kyle or Dana for a dump with the correct ids already stored.
• The branch introduces some new environment variables for email/Facebook/Google auth. Blake, you may have some opinions about how you want to handle these in the repo, and we're happy to make changes to align with your expectations and preferences here.
• If you're wondering why the craft/generator dev dependency is needed for auth.... it's not, and should have been on a different branch. We'll need it soon though, so if you can forgive me for including it in this PR I would appreciate it. 🥲