IO-3096 Add indexes for notifications.

hasura/migrations/1741904805838_run_sql_migration/down.sql

@@ -0,0 +1,3 @@
+-- Could not auto-generate a down migration.
+-- Please write an appropriate down migration for the SQL below:
+-- CREATE INDEX idx_notifications_associations_not_read ON notifications(associationid, read) where read is null;