Finish features for v2 release

[jsheunis]

The project readme has been updated with the following:

📢 A new catalog is coming...
We're working on a newer, leaner, more modular, and more interoperable solution to the same challenge that the current datalad-catalog aims to address. This new development is taking place within the broader context of making DataLad datasets interoperable with linked and semantic (meta)data. For more background, see psychoinformatics-de/datalad-concepts#115. To keep up to date, follow progress at psychoinformatics-de/datalad-concepts, psychoinformatics-de/shacl-vue, and in the new development branch. Because of this redirected focus, datalad-catalog itself will be downscaled by focusing on maintenance and assessing the priority of new features on a case-by-case basis.

Working towards that, I think it is sensible to finish up outstanding issues / PRs and create a new stable release to be maintained. Issues have already been categorized according to how important they might be for the new release vs for future use, here: #470