♻️ Make the media cleaning mechanism on file-gc task more efficient

Replaces the use of db/cursor with db/plan, that teorethically allows
processing large results without consuming all result set in memory

backend/test/backend_tests/helpers.clj

@@ -62,7 +62,7 @@
 (def default
   {:database-uri "postgresql://postgres/penpot_test"
    :redis-uri "redis://redis/1"
-   :file-snapshot-every 1})
+   :auto-file-snapshot-every 1})
 
 (def config
   (cf/read-config :prefix "penpot-test"