add glob parsing to asdf-autoschemas directive

[CagtayFabry]

For larger collections of schemas I wanted to simplify doc creation and tried to get the :glob: option to work with asdf-autoschemas but got nowhere (would seem like an elegant solution).
I managed to get it to work with some "glob-handling" (using pathlib.Path.glob) additions to creating the schema files and doctree.

So instead of specifying all files

.. asdf-autoschemas::

   unit/unit-1.0.0
   unit/defunit-1.0.0
   unit/quantity-1.1.0

the following would get extended to all yaml schemas in unit/

.. asdf-autoschemas::

   unit/*

Is this something you would like to see added in sphinx-asdf?
I'm leaving this PR in case anyone wants to give it a try, code would certainly need some cleanup

[eslavich]

I like the idea, but I think we'll want to use asdf library functions to list available schemas and perform the glob matching. That will be easier once asdf 2.8 is released.