Feature request: Add LTM support

LTM support has been added to Ardupilot firmware recently. It‘s an ultimately lightweight telemetry protocol that allows to downlink the most vital flight data (position, attitude, status, navigation) at 1200 / 2400 baud while still providing update rates of 5-10 Hz.
Due to its design it is particularly suitable for long range downlink telemetry over AV audio, using a simple FSK modem, without the need for additional radio / HF components.
On the ground side, it is frequently used for antenna tracking or simple ground-based data display (Ground-OSD).
However, the list of GCSes that natively support LTM is somewhat limited, actually there’s only one linux-based app still being actively developed (mwptools) as to my knowledge (https://github.com/stronnag/mwptools).

Adding LTM support to MissionPlanner would allow for seamless integration of this streamlined telemetry protocol into the ardupilot environment.

Start by reviewing Mission Planner’s existing telemetry integrations and the LTM protocol as described in the issue, using mwptools as a reference for native LTM support. Done means Mission Planner integrates LTM with the ArduPilot environment and supports the described telemetry use cases; the issue does not name specific files or tests.

Written by the indexing model from the issue text.