Update stack terminology to package

[hasheddan]

Description of your changes

This updates the packaging machinery to use package terminology instead of stack-package. It also updates examples to use ClusterPackageInstall instead of the soon to be deprecated ClusterStackInstall.

Fixes #8

See https://github.com/crossplane/provider-gcp/pull/228 for a similar PR

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.
• [x] Updated any relevant documentation, examples, or release notes.
• [ ] Updated the dependencies in app.yaml to include any new role permissions.
• [ ] Updated the stack resources documentation to include any new managed resources or classes.