get_full_name optional on AbstractBaseUser

[rcjohnson]

https://github.com/airbrake/pybrake/blob/f50658879447d142e490bd23297c34144d62222e/src/pybrake/middleware/django.py#L124 -> references get_full_name(), but per https://docs.djangoproject.com/en/4.2/topics/auth/customizing/ get_full_name is optional. Either update the documentation for Airbrake to make it clear that this method must be implemented, or better, update this line to check for the method and workaround cases when get_full_name is not implemented (e.g. teams with custom user models.)

[rcjohnson]

For context, if this method is missing Airbrake throws an error when trying to log errors seemingly preventing it from actually logging to Airbrake.