Alias only_fields as fields and exclude_fields as exclude

[jkimbo]

To make it easier for developers who have used Django REST Framework before, change only_fields to fields and exclude_fields to exclude so that it matches the ModelSerializer: https://www.django-rest-framework.org/api-guide/serializers/#specifying-which-fields-to-include

only_fields and exclude_fields will still work and we can drop them in a future release.

This PR also includes type checking on the options and support for the __all__ value to select all fields (which mirrors DRF).

Questions

In a future I think we should enforce that either fields or exclude should be required on all DjangoObjectTypes. What you think @phalt @zbyte64 @patrick91 @mvanlonden @dopeboy ?

Also do you think we should start logging PendingDeprecationWarning for only_fields and exclude_fields?

[zbyte64]

👍 for deprecating "only_fields", to quote the zen of python: "There should be one-- and preferably only one --obvious way to do it."

[jkimbo]

@zbyte64 I agree. I've updated the PR to start raising PendingDeprecationWarnings if only_fields and exclude_fields are used. They can be increased to DeprecationWarnings in v3.

[jtratner]

+1 to requiring that you specify either fields or exclude!