Temporary password

This PR adds the temporary password API to the wrapper. Pretty vanilla, just added it to the client and added a response class.

One thing that is different: there is no model class - it felt too heavy handed when all this needs to pass back is a single string. The `response#model` method returns just the new temp password, and I aliased `temp_password` to `model` so you can use the response data as such:
```ruby
response = Cb.user.temporary_password('external_id')
response.temp_password # => 'lol-temp-pass-string'
```