Include actor start count in activation stats (#2274)

Author: rogeralsing

tests/Proto.Cluster.PartitionIdentity.Tests/PartitionIdentityTests.cs

@@ -137,7 +137,7 @@ PartitionIdentityLookup.Send send
         var receivedActivationRequests = activationRequestsReceived;
         var forwardedActivationRequests = activationRequestsForwarded;
         var activationStats =
-            $"sent {sentActivationRequests}, received {receivedActivationRequests}, forwarded {forwardedActivationRequests}";
+            $"sent {sentActivationRequests}, received {receivedActivationRequests}, forwarded {forwardedActivationRequests}, started {totalStarts}";
 
         _output.WriteLine(
             $"{totalCalls} requests, {restarts} restarts, {receivedActivationRequests} activation requests against " +