Start Mock Server

๐Ÿ‘จโ€๐Ÿ’ผ Since we have the mock server going, our OAuth integration mocks in will handle requests made by the remix-auth-github during our tests. But that's just got our happy-path stuff. We need to test the unhappy-path stuff too. Let's get to that next.
๐Ÿงโ€โ™‚๏ธ I'm going to add another utility for us called assertToastSent. Basically, there are several spots in where we redirect the user and pop up a toast for them. We want to test that functionality. You can write it yourself if you like (check out for how it works), or you can check my changes.

No tests here ๐Ÿ˜ข Sorry.