Application-level backup

We should have a way to be able to back up and restore data on a periodic basis. This could be an:

- API
- where we are able to specify which packages/resources to back up along with their fingerprints
- federated data
- where we dump the package/resources and their fingerprints to JSON, commit them to a github repo keyed by purl
- the client would check to see which repos are available for pulling, pull in the changes, and then create packages/resources from the data