Custom DIY device hardware model identifier based on @NanoVHF schematics

[NanoVHF]

Hello.
Recently, the problem with the lack of support for c1268 chips was found out. (https://meshtastic.discourse.group/t/sx1268-modules-are-not-yet-supported/3659/4)
A colleague of mine did support and submitted some pull requests with support for the new SX1268 module (#865) and reserved a name for the new homemade device (meshtastic/protobufs#25).

We propose to make a separate section in platforms.ini and configs for self-made devices "Meshtastic-DIY".
It is also planned to introduce support for new CC68 chips for the maximum number of supported LoRa devices.

[osmanovv]

Link to Meshtastic-DIY project discussion https://meshtastic.discourse.group/t/meshtastic-diy-project/3831

[osmanovv]

Settings for building it as separate board configuration: #870

Declare default_envs = meshtastic-diy-v1 in platformio.ini [platformio] section.