Discoverability of resources (especially atlases)

[oesteban]

As @bthirion reported here https://github.com/nilearn/nilearn/issues/3074#issuecomment-980110269 right now there discoverability of resources (other than template names) is low.

One, of course, could leverage the pyBIDS dependency and execute get_atlases (I'm not even sure this is right), and would get a list of, generally, acronyms.

Further problems include that atlases are not allowed to carry custom licenses, so the overall template's license covers everything.

To improve the discoverability of atlases, at least, it would be interesting to make it require that atlas have some atlas-<entity-value>_description.json at the top of the template. This description file would collect information like the template_description.json file, stating license, authors to credit, papers, and a fully developed name because most of the atlases are denoted by acronyms.

Finally, the Python client could implement as well some get_atlases like the get_templates, and return pairs (atlas ID and full descriptive name).