feat: Automatically set MDX client_protocol_type=TLS for MySQL connections. (#2207)

* feat: Automatically set MDX client_protocol_type=TLS for MySQL connections.

When a Cloud SQL instance supports Metadata Exchange, the MySQL socket factory will 
automatically set MDX client_protocol_type=TLS. This will ensure that the password
auth protocol works correctly. 
See also #2200 and GoogleCloudPlatform/cloud-sql-proxy#2317

Author: hessjcg

jdbc/mysql-j-8/src/main/java/com/google/cloud/sql/mysql/SocketFactory.java

@@ -60,10 +60,9 @@ public <T extends Closeable> T connect(
     T socket =
         (T)
             InternalConnectorRegistry.getInstance()
-                .connect(ConnectionConfig.fromConnectionProperties(props, host));
-    // TODO: When MDX is fully supported by the server,
-    //      add this configuration to automatically set the client protocol type to TLS.
-    //      .withMdxClientProtocolType("tls"));
+                .connect(
+                    ConnectionConfig.fromConnectionProperties(props, host)
+                        .withMdxClientProtocolType("tls"));
     return socket;
   }