Draft: refactor follows and update_nofications indexing

Based on !819

Require tests_api!258

hive/db/sql_scripts/grant_hivemind_user.sql

+GRANT USAGE ON SCHEMA hivemind_app to hivemind_user;
+GRANT USAGE ON SCHEMA hivemind_endpoints to hivemind_user;
+GRANT USAGE ON SCHEMA hivemind_postgrest_utilities to hivemind_user;
+
+GRANT SELECT ON ALL TABLES IN SCHEMA hivemind_app TO hivemind_user;
+GRANT SELECT ON ALL TABLES IN SCHEMA hivemind_endpoints TO hivemind_user;
+GRANT SELECT ON ALL TABLES IN SCHEMA hivemind_postgrest_utilities TO hivemind_user;
+
+ALTER DEFAULT PRIVILEGES IN SCHEMA hivemind_app GRANT SELECT ON TABLES TO hivemind_user;
+ALTER DEFAULT PRIVILEGES IN SCHEMA hivemind_endpoints GRANT SELECT ON TABLES TO hivemind_user;
+ALTER DEFAULT PRIVILEGES IN SCHEMA hivemind_postgrest_utilities GRANT SELECT ON TABLES TO hivemind_user;