main: stop storage_service on shutdown

Just like other services, storage_service needs to be stopped on
shutdown. cql_test_env already stops it, so there is some precedent
for it working. I tested a shutdown while cassandra-stress was
running and it worked okay for a few trials.

main.cc

@@ -851,6 +851,11 @@ int main(int ac, char** av) {
                 std::ref(feature_service), sscfg, std::ref(mm), std::ref(token_metadata),
                 std::ref(messaging), std::ref(cdc_generation_service), std::ref(repair),
                 std::ref(raft_gr), std::ref(lifecycle_notifier)).get();
+
+            auto stop_storage_service = defer_verbose_shutdown("storage_service", [&] {
+                ss.stop().get();
+            });
+
             supervisor::notify("starting per-shard database core");
 
             sst_dir_semaphore.start(cfg->initial_sstable_loading_concurrency()).get();