Added GNC Constants Tracking and Slight Restructuring

[kylekrol]

Added GNC Constants Tracking and Slight Restructuring

Fixes #139.

Summary of changes

• Transitioned to Github Actions
• Updated the build system to rely on a virtual environment install of PIO (see requirements.txt)
• Added a small autocoder to produce the include/gnc/constants.hpp and src/gnc_constants.cpp files
• Added a GNC constants tracking mechanism that piggybacks off of flight software
• The idea here would be the constants tracker in flight software is still the one source of truth in terms of what constants exist and what there values in initialized to

Ptest Effects

NA

Testing

All changes were simply cosmetic. Testing infrastructure was only refactored.

Constants

The value of each constant remained the same but this is the tracking infrastructure.

Documentation Evidence

See inline documentation and the updated README. More documentation, however, should be written about the constants format and autocoder.

[kylekrol]

Did you get to check if FSW catches all the constants?

Did not - although I can go ahead and run it to see. I will tie up those loose ends when integrating the changes into flight software!