DDS: Add new publisher for SITL state

[neo-0007]

estimated state may not be the best for ros visualization and integration
publishing the actual state of a vehicle in SITL
data source : sitl_fdm
publishes to a ros topic : ap/sim/groundtruth
uses a custom msg defined in ardupilot_msgs/msg/GroundTruth

addresses #31995

published data example:

header:
  stamp:
    sec: 1770662102
    nanosec: 107569000
  frame_id: base_link
latitude: -35.3632625
longitude: 149.1652378
altitude: 640.57
position:
  x: 0.03631216660141945
  y: -0.04452753812074661
  z: 56.56999969482422
orientation:
  x: 5.720143008147716e-07
  y: -0.0005015750066377223
  z: -0.08593031018972397
  w: 0.9963010549545288
linear_velocity:
  x: -0.0002664405037648976
  y: -0.0038611870259046555
  z: -1.4962866306304932
angular_velocity:
  x: -0.002559196618829168
  y: -0.0018246009584869244
  z: 0.0006470874775403243
---
header:
  stamp:
    sec: 1770662102
    nanosec: 130893000
  frame_id: base_link
latitude: -35.3632625
longitude: 149.1652378
altitude: 640.54
position:
  x: 0.03631216660141945
  y: -0.04452753812074661
  z: 56.53999710083008
orientation:
  x: 1.0811620086315088e-05
  y: -0.0005204897606745362
  z: -0.08592288941144943
  w: 0.9963016510009766
linear_velocity:
  x: -0.0002848515287041664
  y: -0.003613394685089588
  z: -1.4960895776748657
angular_velocity:
  x: 0.0025319195036645203
  y: 0.0014568570358329536
  z: 0.0006169906365636676

Tested on SITL

Since i am exploring the ardupilot DDS interface this is my first contribution in this area , took a lot of reference from other code . So may require changes , feedback are very much appreciated. Thanks !

[tizianofiorenzani]

See my comments

[neo-0007]

@tizianofiorenzani Thanks for the review.
I did the conversions accordingly and added comments like others for clarity .

[tizianofiorenzani]

LGTM