AP_DDS: Publish all available GPS instances

[tizianofiorenzani]

Allow all GPS instances to be published on the /ap/navsat topic. All instances are published, each with their instance represented in the header.frame_id field.

This approach follows what has been already implemented for the /ap/battery topic.

Test

Simulation parameters need to be updated in order to enable a second GPS instance to be found.

• GPS2_TYPE = 1
• SIM_GPS2_ENABLE = 1
• Restart the simulator and micro-ros.
• On another terminal, publish the topic with: ros2 topic echo /ap/navsat

---
header:
  stamp:
    sec: 1741022473
    nanosec: 424456000
  frame_id: '0'
status:
  status: 2
  service: 1
latitude: -35.36326217651367
longitude: 149.1652374267578
altitude: 584.0899658203125
position_covariance:
- 0.09000000357627869
- 0.0
- 0.0
- 0.0
- 0.09000000357627869
- 0.0
- 0.0
- 0.0
- 0.09000000357627869
position_covariance_type: 2
---
header:
  stamp:
    sec: 1741022473
    nanosec: 424456000
  frame_id: '1'
status:
  status: 2
  service: 1
latitude: -35.36326217651367
longitude: 149.1652374267578
altitude: 584.0899658203125
position_covariance:
- 0.09000000357627869
- 0.0
- 0.0
- 0.0
- 0.09000000357627869
- 0.0
- 0.0
- 0.0
- 0.09000000357627869
position_covariance_type: 2
---

[Ryanf55]

If the GPS goes unhealthy, we still need to publish it. Existing problem.