Ability to pass extra data during email signup

[albertowar]

The Javascript SDK provides the ability to send and attach metadata to an user during creation through the options.data field.

At the moment, the EmailAuth doesn't provide the ability to do the same thing.

I was wondering if you would considering adding a prop that can be used to pass through metadata to that the signUp call.

If that sounds like a good idea to you, I'm happy to give it a try and submit a PR.