doc: Mention dispatcher shutdown timeouts (#28527)

akka-docs/src/test/scala/docs/dispatcher/DispatcherDocSpec.scala

@@ -88,6 +88,22 @@ object DispatcherDocSpec {
       throughput = 100
     }
     //#my-thread-pool-dispatcher-config
+    
+    //#my-dispatcher-with-timeouts-config
+    my-dispatcher-with-timeouts {
+      type = Dispatcher
+      executor = "thread-pool-executor"
+      thread-pool-executor {
+        fixed-pool-size = 16
+        # Keep alive time for threads
+        keep-alive-time = 60s
+        # Allow core threads to time out
+        allow-core-timeout = off
+      }
+      # How long time the dispatcher will wait for new actors until it shuts down
+      shutdown-timeout = 60s
+    }
+    //#my-dispatcher-with-timeouts-config
 
     //#affinity-pool-dispatcher-config
     affinity-pool-dispatcher {