use cases:
- extra commit information (e.g., signed-off-by, etc.)
- store checksums of tarballs (which are mapped to revisions), as we cannot necessarily reproduce them (even though we can reproduce the checksums of full tarball //contents//)
proposed postgres datatype: json/jsonb
we will also need to document the schema (e.g., field names) of how we intend to use the field in practice