docs: Add feature design guidelines
Description
This adds a feature design guide to the contribution guidelines. It's intended to be a reference point when adding a new command or sub-command.
Related Issues
N/A
How has this been tested?
N/A
Screenshots (if appropriate):
N/A
Types of changes
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Bug fix (non-breaking change which fixes an issue) -
New feature (non-breaking change which adds functionality) -
Breaking change (fix or feature that would cause existing functionality to change) -
Documentation -
Chore (Related to CI or Packaging to platforms) -
Test gap