Customer Rating and review changes

backend/app/electronics/db/migrations/0007_rating_breakdown.sql

@@ -0,0 +1,4 @@
+-- Star breakdown of a listing's ratings, exactly as the source states it:
+-- {"5": 612, "4": 300, "3": 80, "2": 20, "1": 12}. NULL when the source does
+-- not publish one - never derived from the few review texts we hold.
+ALTER TABLE elec.source_listing ADD COLUMN rating_breakdown JSONB;