Enable Multiple H2 connections in BenchmarkApp (#808)

testassets/BenchmarkApp/Startup.cs

@@ -34,6 +34,7 @@ namespace BenchmarkApp
                 { "Routes:0:ClusterId", "cluster" },
                 { "Routes:0:Match:Path", "/{**catchall}" },
                 { "Clusters:cluster:HttpClient:DangerousAcceptAnyServerCertificate", "true" },
+                { "Clusters:cluster:HttpClient:EnableMultipleHttp2Connections", "true" },
             };
 
             var clusterCount = 0;