PASSWORDLESS_USER_MOBILE_FIELD_NAME doesn't work for anything other than 'mobile'

[jws]

If you override PASSWORDLESS_USER_MOBILE_FIELD_NAME from the mobile default, the API serializer is not aware and will fail on validate.

https://github.com/aaronn/django-rest-framework-passwordless/blob/dcf520fc29d7a2af2d366b80e5af0f7753c8ab20/drfpasswordless/serializers.py#L54

The serializer should use PASSWORDLESS_USER_MOBILE_FIELD_NAME for:

• querying against User model
• request payload
• (possibly) even the registered urls