MFD Crossbow tracker integration

[wvarty]

Overview

This pull request introduces an integration for the MFD Crossbow tracker into the ExpressLRS Backpack project.

Integration Details

Hardware:

• TX module with a TX Backpack
• A receiver flashed with one of the MFD Crossbow Backpack targets
• MFD Crossbow

Telemetry Transmission:

• The Backpack receiver binds to the TX Backpack using the usual: bind phrase or Bind menu in LUA.
• The aircraft’s GPS telemetry is forwarded from the TX Backpack to a Backpack receiver (an ELRS receiver flashed with the Backpack MFD target) via ESPNOW.
• The telemetry data is converted from CRSF to MAVLink for optimal performance with the Crossbow.
• The Backpack receiver UART is wired to the Crossbow, and sends MAVLink at 115200 baud to the tracker
• That's pretty much it! Tracker tracks the craft. Great for digital users!

Big thanks to:

• Bonafide Pirate
• Shannon Baker
• Erwin Quilloy

for their exceptional testing and feedback 💪

[wvarty]

To test:

1. Ensure that your TX module and TX backpack are up to date with the latest official release
2. On your TX module, in LUA, set your telem ratio to 1:2 or 1:4, so that the tracker will receive regular GPS updates (slower telem ratios will cause the tracker to drop to 0 sats).
3. On your TX module, in LUA, go to the Backpack folder, and set Telemetry to On
4. Flash a receiver as a Backpack receiver, with the MFD Crossbow target. From the Configurator, choose the Backpack menu, select GIT BRANCH, find the tracker-backpack branch, choose the MFD Crossbow Antenna Tracker Backpack Device category, and select the Generic xxxx target to match the ESP chip on your receiver. Enter your bind details flash as per normal.
5. Wire the freshly flashed Backpack receiver to the Crossbow: 5V to 5V, GND to GND, and wire the tx pad on the receiver to the rx pad on the tracker.
6. In the Crossbow menu, setup either the L-port or R-port (depending on the one you used) as MAVLink protocol, at 115200 baud.
7. Power up a craft that has a GPS onboard, establish a link, and ensure that the tracker is reporting DLINK=100%

[wvarty]

Requested class changes made.