Allow to change cipher suite (#1381)

* Allow to change the used Cipher Suite

* Also added cipher suite to the mqtt client part

* Added ConfigureAwait

Source/MQTTnet/Server/Options/MqttServerTlsTcpEndpointOptions.cs

@@ -24,5 +24,9 @@ namespace MQTTnet.Server
         public bool CheckCertificateRevocation { get; set; }
 
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12;
+        
+#if NETCOREAPP3_1 || NET5_0_OR_GREATER
+        public System.Net.Security.CipherSuitesPolicy CipherSuitesPolicy { get; set; }
+#endif
     }
 }