add extra_configs support for local platformio env

[tstibor]

Add platformio_custom.ini as an extra_configs entry so developers can define personal board environments (e.g. [env:m5stampfly]) without modifying the tracked platformio.ini. The file is gitignored to keep local configs out of the repository.

Example:

$ cat platformio_custom.ini
[env:M5STAMPFLY]
board = esp32-s3-devkitc-1
platform = espressif32
framework = arduino
monitor_filters = esp32_exception_decoder
build_flags =
    -D ARDUINO_USB_MODE=1
    -D ARDUINO_USB_CDC_ON_BOOT=1

[qqqlab]

I don't mind if you add the m5stampfly config directly in platform.ini (and keep the platform_custom.ini as well)

The idea is to support stampfly at some point.

Todo:

• VL53L3 - driver available, but needs enable pin
• PMW3901 - driver available, but need sync/mutex
• INA3221
• ESP-NOW remote

We could add a stampfly specific example or hack mf lib for stampfly specific stuff... Probably use first option: Do the PMW3901 update in imu_loop(), and set VL53L3 enable pin in setup()

What are you doing for rc radio?

This is my work-in-progress setup:

Black port -> openlog sdcard
Red port -> elrs receiver

[tstibor]

Today finally the HY2.0 cable arrived. I had not such a cable. My plan is connect a spare TBS CRSF nano to it.
Once everything is soldered I will look at the PMW3901 sync/mutex first.