Slow creation with dynamic STAC catalogs

[TomAugspurger]

In

intake-stac/intake_stac/catalog.py

Line 123 in b145149

for subcatalog in self._stac_obj.get_children():

, intake-stac will recurse into child objects. This will end up making many HTTP requests for large, dynamic STAC catalogs served over a STAC API like https://planetarycomputer.microsoft.com/api/stac/v1.

I believe that all the necessary information is provided at the https://planetarycomputer.microsoft.com/api/stac/v1/collections endpoint. https://github.com/stac-utils/pystac-client handles all the logic for interacting with STAC APIs efficiently (it has subclasses for pystac.Collection, etc.). Something like

pystac_client.Client.open("https://planetarycomputer.microsoft.com/api/stac/v1/").get_collections()

should efficiently get the child collections for APIs that implement the /collections endpoint (I'm unsure about child catalogs; we don't use them).

Might have some overlap with #66.