Check for untracked and staged files in check-diff

[hasheddan]

Signed-off-by: hasheddan georgedanielmangum@gmail.com

Description of your changes

Currently check-diff will miss untracked and staged files. This can be a problem if new types are added and newly generated files (e.g. CRDs) are not checked in. See https://github.com/crossplane/crossplane/pull/1490 for implementation in c/c.

Checklist

I have:

• [x] Run make reviewable to ensure this PR is ready for review.
• [x] Ensured this PR contains a neat, self documenting set of commits.
• [ ] Updated any relevant documentation, examples, or release notes.
• [ ] Updated the dependencies in app.yaml to include any new role permissions.
• [ ] Updated the package resources documentation to include any new managed resources or classes.

[hasheddan]

@negz can you merge this one?

[hongchaodeng]

@hasheddan Let me do the merge for you :)

[hasheddan]

@hongchaodeng thank you!