Python client for STAC Catalogs and APIs!

An iterable-style DataPipe to make STAC API queries! Uses pystac-client to perform the STAC API Item Search. Included a doctest that does a STAC API search which returns an iterable list of STAC item objects. Added a new section in the API docs and an intersphinx mapping.

Ensure that a spatiotemporal query can be made to a STAC API /search/ endpoint to produce an instance of a pystac_client.ItemSearch object containing pointers to multiple pystac.Item objects. Also removed a for-loop that was accidentally added after a yield statement.

Decided that it is cleaner to pass in all the STAC API query parameters via the source_datapipe, rather than through both the source_datapipe and kwargs. The kwargs can then be kept for keyword arguments into pystac.Client.open. Documented some example parameters for pystac_client.Client.search and pystac_client.Client.open. Updated the unit test and doctest, adding a teaser way to sign planetary_computer assets inplace too!

Ensure that parameters such as authentication keys can be passed to pystac_client.Client.open. Using a fake API key for Radiant MLHub, which can only take us so far as to getting a title and description.

Fix Continuous Integration failure because jsonschema had to be installed but it is an optional dependency.

Bump oauthlib from 3.2.0 to 3.2.1

Move pystac and pystac-client to a dedicated `stac` extras section for spatiotemporal dependencies! Also updated index page with instructions on installing these STAC dependencies.