Add board def for Adafruit Feather ESP32-C6

[tyeth]

This adds the Adafruit Feather ESP32-C6 (4mb variant no psram).

About to test it and then will make non-draft. Also need to confirm the board define is correct.

Should match up to https://github.com/espressif/arduino-esp32/tree/master/variants/adafruit_feather_esp32c6

[valeros]

Hi @tyeth, thanks for the PR. This board was added in the Arduino core v3.0.3 which is currently unsupported, see #1225.

[tyeth]

Thanks @valeros
I did see that this would be the case last night when looking at another board PR that needs 3.0.3 and was left open.

Guess this will sit here for a while, but it's possibly useful for our testing (and others).