Glob search for collection entries in a folder and all subfolders

[zachleat]

Currently all entries in a Netlify CMS collection need to live in the same top-level folder. It’d be awesome if it could search inside of a folder and return all *.md files in there.

Relatedly, it would be even better if the Collection view showed the folders too (e.g. my collection is named pages: /admin/#/collections/pages). And even super better if the Relation widget showed those folders too (but that is asking a lot)

This is somewhat related to #3227

[erezrokah]

The use case for this issue should be covered in #3227
Please comment if that feature doesn't satisfy the requirements.