Add ability to configure social and custom domains

[mraible]

Let's face it, configuring social login and custom domains is kinda painful because there are so many steps. Let's automate them with the CLI!

Maybe Cloudflare has an API we can use to automate our guide? I'm not sure.

Sample commands:

okta add custom-domain <URL>
okta add social-login

Related: what if okta add was a way of adding plugins? Kinda like Oh My Zsh's plugins? It might be cool to have an architecture where developers can extend the CLI for their own needs. I could see it being used by DevOps teams to automate adding/removing apps as part of their CI process.