Add Optical Flow for Proto 2

[mtfunder]

Rationale

• We decided an optical flow module may be a better way of tracking the ground than a wheel encoder (easier to integrate). Both Hardware and Firmware will need to work to implement an OFM.

What done looks like

• All new parts added to PartsBox
• Confluence page updated to reflect the design decisions.

Stakeholders / Contacts

• @mtfunder

Additional Information

• We don't necessarily need to use the data in real time at this stage.
• Will try to find a simple module with good documentation.

[mtfunder]

@priyajakhar @HaydenMcCleary

Here is the module we are getting:
https://irlock.com/products/here-flow?srsltid=AfmBOoo2X3UUmHk8fuaWWT1rHI3TfZxKSRnAn2vStoI2btRPEHxDdZjT

Basic Docs:
https://docs.cubepilot.org/user-guides/flow-senor/here-flow

I think this is their onboard firmware source?
https://github.com/CubePilot/Flow

And here is the Ardupilot Hereflow header file (this is probably the most relevant):
https://github.com/ArduPilot/ardupilot/blob/master/libraries/AP_OpticalFlow/AP_OpticalFlow_HereFlow.cpp

[mtfunder]

Hardware done but software intergation pending afaik.