Add support for publishing position data from MQTT

[samuelthoren]

The current implementation can receive MQTT messages and then publishes a message of type std_msgs/msg/Empty.

This PR extends that functionality and adds support for sending any type of message. This PR adds the support for sensor_msgs/msg/NavSatFix and sends the latitude, longitude, and altitude to ROS.

Relevant part from params.yaml:

mqtt2ros: # Object specifying which MQTT topics to map to which ROS topics
        mqtt_topics: # Array specifying which ROS topics to bridge
          - position_sender # The MQTT topic that should be bridged, corresponds to the sub-object in the YAML
        position_sender:
          ros_topic: position_sender/position # ROS topic on which corresponding MQTT messages are published
          msg_type: sensor_msgs/msg/NavSatFix
          advanced: # Optional settings for each topic
            mqtt:
              qos: 1 # [0] MQTT QoS value
            ros:
              queue_size: 1 # [1] ROS publisher queue size