DDS: Validate ROS_DOMAIN_ID environment is the same as DDS_DOMAIN_ID

[Ryanf55]

Feature request

Is your feature request related to a problem? Please describe.

If someone sets the ROS_DOMAIN_ID and it doesn't match their DDS_DOMAIN_ID, they can't communicate with the vehicle over DDS

Describe the solution you'd like

In sitl.launch.py , use pymavlink to read the DDS_DOMAIN_ID param, and issue a warning if it doesn't match the environment variable ROS_DOMAIN_ID

Describe alternatives you've considered

The wiki explains this, but people miss it from time to time

Platform [ x ] All [ ] AntennaTracker [ ] Copter [ ] Plane [ ] Rover [ ] Submarine

Additional context