fix(server): created user in update table should not have defualt value (#8134)

packages/backend/server/migrations/20240826033024_editor_record/migration.sql

@@ -6,7 +6,7 @@ ALTER TABLE "snapshots" ADD COLUMN     "created_by" VARCHAR,
 ADD COLUMN     "updated_by" VARCHAR;
 
 -- AlterTable
-ALTER TABLE "updates" ADD COLUMN     "created_by" VARCHAR DEFAULT 'system';
+ALTER TABLE "updates" ADD COLUMN     "created_by" VARCHAR;
 
 -- AddForeignKey
 ALTER TABLE "snapshots" ADD CONSTRAINT "snapshots_created_by_fkey" FOREIGN KEY ("created_by") REFERENCES "users"("id") ON DELETE SET NULL ON UPDATE CASCADE;