Expose measured force torque data

[thettasch-samxl]

An addition to expose the measuredForce field from the abb.egm.EgmRobot protobuf message, to allow downstream code to read out the force-torque sensor data.

The code should be compatible with both 6DOF and 1DOF sensors, although I have only been able to test it with a 6DOF sensor. Behaviour should remain unchanged if the measuredForce field is empty.

I have already made the extra additions to abb_egm_rws_managers and abb_ros2 to allow the force torque data from a real robot with 6DOF FT sensor to be published by a standard ForceTorqueSensorBroadcaster. I will open PR's on those repositories once/if this change is accepted here.

Note: this is for external FT sensors, not for internal joint-torque measurements as discussed in #86.