Migrate to latest, split python-social-auth.

PSA was monolothic, now split, with new features, like
a DB-backed partial pipeline. FB OAuth2 version also upped.

Partial pipelines don't get cleared except when necessary.
They persist for special cases like change of browser while
still mid-pipeline (i.e. email validation step).

Refactor, cleanup, and update of a lot of small things as well.

PLEASE NOTE the new `social_auth_partial` table.

openedx/features/enterprise_support/api.py

@@ -320,7 +320,7 @@ def insert_enterprise_pipeline_elements(pipeline):
         'enterprise.tpa_pipeline.handle_enterprise_logistration',
     )
     # Find the item we need to insert the data sharing consent elements before
-    insert_point = pipeline.index('social.pipeline.social_auth.load_extra_data')
+    insert_point = pipeline.index('social_core.pipeline.social_auth.load_extra_data')
 
     for index, element in enumerate(additional_elements):
         pipeline.insert(insert_point + index, element)