Use OAFeat items endpoint for get_item

[duckontheweb]

The CollectionClient class relies on the inherited Collection.get_item method to fetch an Item by ID. This results in looping over all the Items in the Collection until the one with the correct ID is found, which can be extremely inefficient for large collections. For example, using CollectionClient.get_item to fetch the ref_landcovernet_v1_source_35KNT_04_20180105 Item from the the ref_landcovernet_v1_source Collection in Radiant MLHub is still running after 10 minutes for me.

The OGC API - Features spec provides a /collections/{collection_id}/items/{item_id} endpoint that can be used to fetch an Item directly by ID. Making a request for the example Item above using this endpoint resolves in under a second.

It seems worthwhile for CollectionClient to override the inherited get_item method to use this endpoint if the proper conformance classes are present and fall back to using the inherited method if they are not.

[duckontheweb]

cc: @KennSmithDS

[matthewhanson]

Thanks @duckontheweb , we will add a CollectionClient.get_item function in the next release.