feat: ELRS backpack support for OSD

[kirek007]

This pull request introduces the ELRS Backpack integration, which sends messages to the OSD to show lap times right in front of you!

Showcase: https://streamable.com/epdhtc

Todo:

• Move esp backpack support to own file
• Implement simple lap counter
• Add race start / stop messages
• Add message position configuration
• Add message customisation (last lap, best lap, lap count)

ELRS Bind Phrase Configuration:

• data/index.html: Added a hidden input field for the ELRS bind phrase.
• data/script.js: Added JavaScript to handle the ELRS bind phrase input and save it in the configuration. [1] [2] [3]
• lib/CONFIG/config.cpp: Updated configuration handling to include the ELRS bind phrase. [1] [2] [3] [4] [5]
• lib/CONFIG/config.h: Added the ELRS bind phrase to the configuration structure and class. [1] [2]

MSP Library Integration:

• lib/MSP/Readme.md: Added a note about the source of the MSP library files.

[suzrik]

This is exactly what I was looking for. Are you going to finish this? Maybe I can help somehow?

[kirek007]

This is exactly what I was looking for. Are you going to finish this? Maybe I can help somehow?

I would like to finish it, but currently it requires more work than I can handle.
Due to the current implementation of how lap time is handled internally, it's not possible to show correct times on OSD.
Feel free to test it and code part that are missing

[phobos-]

I've been testing it for some time now, looks good so far but cannot be merged in the current state.