Update OAuthAuth Class Docstring
Update OAuthAuth Class Docstring

The previous Docstring was miss understanding when it says:
- "Setting name is created from current backend name (all uppercase) plus _EXTRA_DATA." which leads to <uppercase_current_backend>_EXTRA_DATA.

I'm proposing this change to explicitly include the SOCIAL_AUTH_ prefix on the Setting entry, which leads to SOCIAL_AUTH_<uppercase_current_backend>_EXTRA_DATA.

Also I've tested and just EXTRA_DATA but I understand that its too generic.
python-social-auth/social-core,python-social-auth/social-core