There's a dedicated forward_service::shutdown() method that's defer-scheduled in main for very early invocation. That's not nice, the fwd service start-shutdown-stop sequence can be made "canonical" by moving the shutting down code into abort source subscription. Similar thing was done for view updates generator in 3b95f4f107
refs: #2737
refs: #4384Closesscylladb/scylladb#15545
* github.com:scylladb/scylladb:
forward_service: Remove .shutdown() method
forward_service: Set _shutdown in abort-source subscription
forward_service: Add abort_source to constructor