Add keywords to Zenodo archive to fix dataset validation issue

[e-belfer]

Right now datasets can be archived to Zenodo without keywords. In the datapackage.json file for each dataset, this leaves an empty keywords: [] field. When we run pudl_datastore on these archives, we are left with a validation error that prevents data extraction. To fix this issue, do the following:

• add keywords to all datasets missing them in pudl.metadata.constants
• remake environment in pudl-archiver
• re-run archives
• When making a new dataset, assert keywords exist pudl-archiver#167

In the long term, this should be more simply addressed through #1684. Partial duplicate of issue #80 in pudl-archiver repo.