added dedicated footprint for measuring Actor memory footprint (#5047)

Author: Aaronontheweb

src/benchmark/Akka.Benchmarks/Actor/ActorMemoryFootprintBenchmark.cs

@@ -0,0 +1,51 @@
+//-----------------------------------------------------------------------
+// <copyright file="ActorMemoryFootprintBenchmarks.cs" company="Akka.NET Project">
+//     Copyright (C) 2009-2021 Lightbend Inc. <http://www.lightbend.com>
+//     Copyright (C) 2013-2021 .NET Foundation <https://github.com/akkadotnet/akka.net>
+// </copyright>
+//-----------------------------------------------------------------------
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading.Tasks;
+using Akka.Actor;
+using Akka.Benchmarks.Configurations;
+using BenchmarkDotNet.Attributes;
+
+namespace Akka.Benchmarks.Actor
+{
+    [Config(typeof(MicroBenchmarkConfig))]
+    public class ActorMemoryFootprintBenchmark
+    {
+        public ActorSystem Sys;
+        public Props Props;
+
+        [GlobalSetup]
+        public void Setup()
+        {
+           Sys = ActorSystem.Create("Bench");
+           Props = Props.Create(() => new TempActor());
+        }
+
+        private class TempActor : UntypedActor
+        {
+            protected override void OnReceive(object message)
+            {
+                
+            }
+        }
+
+        [Benchmark]
+        public void SpawnActor()
+        {
+            Sys.ActorOf(Props);
+        }
+
+        [GlobalCleanup]
+        public async Task Cleanup()
+        {
+            await Sys.Terminate();
+        }
+    }
+}