Add a GDAL-based item creator #555

Job	Run time
macos	10m 51s
without-gdal (-p stac)	33s
doc	2m 22s
without-gdal (-p stac-api)	28s
windows	4m 37s
format	17s
with-gdal (-p stac -F gdal)	2m 16s
with-gdal (-p stac-cli)	1m 44s
without-gdal (-p stac-async)	52s
with-gdal (--all-features)	3m 43s
without-gdal (-p stac-validate)	1m 6s
without-gdal (-p stac-cli --no-default-features)	50s
without-gdal (-p stac -F reqwest)	1m 25s
without-gdal (-p stac -p stac-api -F geo)	57s
without-gdal (-p stac -p stac-api -F schemars)	37s
	32m 38s

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