Add support for the last will

[sumitjat3]

Pull request support request from the issue, which request for the feature adding Last Will and Testament to the MqttConnectOptions.

For more information about Last Will and Testament read here

Example

  val will = Will(
            topic = "last/will/topic",
            message = "Client disconnected unexpectedly",
            qos = QoS.ZERO,
            retained = false
        )

        val connectOptions = MqttConnectOptions.Builder()
            .serverUris(listOf(ServerUri(ip, port))
            .clientId(clientId)
            .userName(username)
            .password(password)
            .cleanSession(false)
            .will(will)
            .keepAlive(KeepAlive(timeSeconds = 30))
            .build()