add publish_odom param

[Rezenders]

I propose adding the parameter publish_odom to indicate whether odometry should be published or not.
I want to reuse this node to publish the map and earth transformations but I don't want to it publish odometry.

I'm using these parameters

/**:
  ros__parameters:
    publish_odom: false
    sensor_names:
    - gps
    sensors:
      gps:
        topics:
          position: 'gps/fix'