refactor follows and update_nofications indexing

Based on !819 (closed)

Require tests_api!258 (merged)

hive/db/sql_scripts/postgrest/bridge_api/bridge_api_does_user_follow_any_lists.sql

@@ -16,11 +16,7 @@ BEGIN
       hivemind_postgrest_utilities.parse_argument_from_json(_params, 'observer', True), True),
     True);
 
-  IF NOT EXISTS (SELECT ha.name FROM hivemind_app.follow_blacklisted fb JOIN hivemind_app.hive_accounts ha ON ha.id = fb.following WHERE fb.follower = _observer_id LIMIT 1) THEN
-    RETURN 'false'::jsonb;
-  ELSE
-    RETURN 'true'::jsonb;
-  END IF;
+  RETURN (SELECT EXISTS (SELECT ha.name FROM hivemind_app.follow_blacklisted fb JOIN hivemind_app.hive_accounts ha ON ha.id = fb.following WHERE fb.follower = _observer_id LIMIT 1))::TEXT::jsonb;
 END
 $$
 ;