Meetups: Implement Firebase Authentication Using Email Link

[justinwongeecs]

Firebase Documentation: https://firebase.google.com/docs/auth/ios/email-link-auth

We need to create a manager of some sort to handle Meetups Firebase Authentication using email link.

How this works:

1. User enters their berkeley email.
2. On the client verify that it ends with @berkeley.edu.
3. If valid, call Firebase API to send verification link to requested berkeley email
4. Configure Firebase Hosting according to Docs
5. Once user clicks on verification link, Firebase will send a deep link. We should parse it call another Firebase API:

if Auth.auth().isSignIn(withEmailLink: link) {
        Auth.auth().signIn(withEmail: email, link: self.link) { user, error in
          // ...
        }
}

6. If valid, redirect to main Meetups page
7. Implement sign out and other relevant authentication logic