Federated login

[jonsmirl]

Amplify's federated support is limited, here is a feature-request I wrote up.
aws-amplify/amplify-js#6300

I've been working though and implementing this in my own app. I would love to see it implemented in a boilerplate. The boilerplate should support Google, Facebook, Apple login.

BTW, so far I have not needed to make changes to Amplify in order to implement this.