Add support for Heltec HRU-3601

[ndoo]

Board is very similar to the Heltec HT-C62 based boards (Heltec HT62 variant) but due to wiring of SK6812 Neopixel LED to GPIO2 it becomes incompatible due to the regular HT-C62 dev board using a simple LED on the same GPIO. Depends on protobufs#521.

Works:

• SK6812 Neopixel on GPIO2
• GXCAS GXHTV3 (SHTC3 compatible)

Not working:

• SX1262 initialization after deep sleep (seems like an issue out of scope of the PR)

Won't fix:

• Battery reading - Board has no voltage divider on VBAT (board has a 1.25mm pitch "JST" style connector and a TP4054 charge IC)
• Main thread LED - Board has no LED on simple GPIO

Board schematic: HRU3601.pdf

[ndoo]

I noticed that the SX1262 does not initialize when the board wakes up from deep sleep, with SX126x init result -2 followed by a critical error.

I've double checked the pins in variant.h against the schematic and it does not appear to be caused by this PR but a regression/issue elsewhere.

[caveman99]

Looks good to me, I'll review the protobuf change now.

[caveman99]

Protobufs are in place now, just need to change from PRIVATE_HW to a unique tag you chose and add the translation to architecture.h of the ESP platform source.

[ndoo]

Rebase on HEAD in an attempt to make CI happy