[NEW] User registration

[rafaelks]

Description

We need to support the API to register a new user.

Documentation: https://docs.rocket.chat/developer-guides/rest-api/users/create.

Progress

• [ ] Registration of the user;
• [ ] Support to custom fields;
• [ ] Unit tests;

[philipbrito]

The documentation link is broken...

[rafaelks]

@filipedelimabrito Fixed now.

[graywolf336]

You'll need to use https://rocket.chat/docs/developer-guides/rest-api/users/register as users.create is for administrators to create new users, not people to register.