Rewrite bundle population script to not download archives from SDA

Created by: ri-pandey

In ticket #102 (closed) we added the functionality to persist bundle metadata in a separate table. In that ticket, we settled on an initial approach for populating bundle metadata, which downloads bundles from the SDA, computes their size, checksum, etc., and uses that info to persist the bundle metadata.

Since downloading all datasets from the SDA can take a long time, we should rewrite this script so that it can populate bundles without needing to download datasets.

poulate_bundles.py was the original script introduced in ticket #102 (closed), which downloaded datasets from the SDA.