set up postgres class

backend/categorisation/categorisation_postgres.py

@@ -0,0 +1,5 @@
+from backend.app.db.connection import db_session
+
+
+class CategorisationPostgres:
+    pass

backend/categorisation/processor.py

@@ -1,2 +1,10 @@
-def process_portfolio() -> None:
+def process_portfolio(portfolio_id: int) -> None:
+    # Get all plans (including scenarios) for all properties in the portfolio
+
+    # For each property, get all compliant plans
+
+    # For each property, find the cheapest compliant plan
+
+    # For each property, set is_default for cheapest compliant plan
+    # If no compliant plans, set it to the cheapest plan
     pass