OPTIONS could easily return the default of a serializer

[john-parton]

This only works if you apply this PR/patch: #8002

If you override rest_framework.metadata.SimpleMetadata as follows, then you get the field default when you do an OPTIONS query.

from rest_framework.fields import empty
from rest_framework.metadata import SimpleMetadata


class Metadata(SimpleMetadata):

    def get_field_info(self, field):
        field_info = super().get_field_info(field)

        if field.default is not empty:
            field_info['default'] = field.default

        return field_info

Like magic, for every field:

Here's my branch with the fix for missing default and the feature to add default to the OPTIONS request: https://github.com/john-parton/django-rest-framework/tree/feature/include-defaults-in-options

Should this feature be the default behavior? I would happily submit a PR

[SchrodingersGat]

I would really benefit from such a feature for the InvenTree project, as well as #8002