Add diffing functionality

It would be really cool to have diffing functionality for bundles, node configs, components, cluster objects. Not something that is planned for the very near term, but definitely something planned for reasonably soon -- it's essentially for building automation.

The issue mentions bundles, node configs, components, and cluster objects, but names no files, tests, or entry points. First map where these objects are represented and how automation currently compares them, then define the supported diff scope and expected output. Done means a settled design and working diffing functionality for the agreed object types.

Written by the indexing model from the issue text.