Improve and fix MAVLink system/component handling

[ES-Alexander]

Building on #1815:

1. Removes redundant MAVLink ID field names from the Data Lake variable IDs
   • e.g. /mavlink/system=1/component=1/HEARTBEAT/base_mode --> /mavlink/1/1/HEARTBEAT/base_mode
   • The system and component designations are already spelled out in the (human-readable) variable name, so don't need to also be included in the (machine-differentiable) variable IDs
   • This also makes them better match the MAVLink paths used in Zenoh in the latest BlueOS betas, which could make for more straightforward integration later (as pointed out by @joaoantoniocardoso)
2. Fixes the legacy variable creation to only apply to the main system's autopilot component
   • Other systems and components were not supported in this style previously, and
   • Including them without the system and component prefix for disambiguation means the values would overwrite from any connected systems and components (which, from past experience, is quite confusing).

[rafaellehmkuhl]

Makes sense!