Add an import/export-to-tar method/feature

It would be convenient (although not terribly necessary) to have an import/export-to-tar feature that exported all the components to a tar file.

The issue names no files, tests, or entry points. Start by mapping how cluster-bundle components are currently assembled and persisted, then clarify the tar archive's import and export behavior; done should mean all components can be exported to and imported from a tar file.

Written by the indexing model from the issue text.