add new param for enhanced stereo sss

[coleshaw]

Looks like there is a new-ish parameter for enhanced stereo during substructure searching: do_enhanced_stereo_sss. Currently, if I try setting that, I get an exception:

self = <django_rdkit.config.Config object at 0x7fffc8214460>
name = 'do_enhanced_stereo_sss', value = True

    def __setattr__(self, name, value):
        if not name in _PARAMETERS:
>           raise AttributeError
E           AttributeError

/usr/local/lib/python3.10/site-packages/django_rdkit/config.py:28: AttributeError

This adds support for setting that value via django_rdkit. Monkey-patching locally with this works when doing searches in Postgres with the RDKit cartridge.