Allow querystring in MqttWebsocketConfig

[alsanrum]

Problem or use case

Hi,
when I try use websockets that need queryString I discovered that the request is bad formatted because the MqttWebSocketInitializer is using URI class only which the serverPath argument.

Preferred solution or suggestions

Add queryString in MqttWebSocketConfig.
Use queryString of the new MqttWeSocketConfig in URI inside of initChannel of MqttWebSocketInitializer class.

Thanks

[SgtSilvio]

Resolved by #336