Implement Register API

[ignacio-chiazzo]

Cloud API released register API.

Steps to implement it:

• [x] Create the methods register and deregister in the file lib/whatsapp_sdk/api/phone_numbers.rb similar to the other two methods (you need to use http POST).
• [x] Add a test file.

See documentation.

[andresyebra]

Could I take this? 🚀

[ignacio-chiazzo]

Sure! @andresyebra. This PR is very similar https://github.com/ignacio-chiazzo/ruby_whatsapp_sdk/pull/58/files

[andresyebra]

@ignacio-chiazzo PR(https://github.com/ignacio-chiazzo/ruby_whatsapp_sdk/pull/65) is still in progress.

[ignacio-chiazzo]

The registered API is in version 0.7.1. Thanks for contributing!