Write Powerhead DSDL datatype

[zbrown23]

In order to properly publish the state of Powerhead, we need to keep track of what we care about, and what we want to make a UAVCAN topic (pub-sub) vs. UAVCAN register (request-response). Topics would probably be stuff like state of charge, current consumption, battery cell voltage, etc. Registers are usually configuration data like the Cyphal node ID or BMS settings.

[Willmac16]

From the Cyphal getting started guide