Debug: Implement UART debug interface

[ETSells]

**Requester: @ETSells **

Describe the solution you'd like
Rev 3 (MAV) uses the STLink-V3Minie as its debugger. This device comes equipped with the standard SWD interface we need for firmware flashing, but also has a virtual COM port (VCP) that can be used as an additional line of communication between the STM32 and a user's computer.

We have a couple of options to take advantage of this:

1. Use it as an additional console interface for terminal communication in case USB breaks (again).
2. Use it as a debug console that we can log to throughout execution with print statement style debugging, etc.
3. Both?

I'm currently inclined to pick option 2, but we can explore others if we want a specific implementation.

Marking for sprint planning 5/26.

Describe alternatives you've considered
Alternative options listed above.

Additional context
N/A

Points of Contact
R3 Project Lead: @ETSells

[ETSells]

This is a good first driver for newer developers (but not an overall "good first issue").

@Bigmouseears could be good for this once the GPS fixes are ready.

[ETSells]

I'm currently implementing module level support, so all you'd have to do is supply the callback that the module takes.