Builds on #3075 and adds the ability to configure the Head Tracking start channel as "EdgeTX" which sends the Pan/Tilt/Roll data back to EdgeTX as trainer data so it can be used in the mixer like any other head tracker.

For this to operate there is a matching EdgeTX PR for configuring the trainer port as Master/CRSF EdgeTX/edgetx#5724.

• Flash EdgeTX with the build from github
• Configure trainer option in EdgeTX
  
• Configure the mixer to output Pan/Tilt/Roll to the channels you desire
  
• Flash this PR to you TX module
• Select EdgeTX as the HT Start Channel in the Backpack menu of the Lua script.
  
• See your channels move in the Channel Monitor screen
  
• Profit 😄