exclude_plaforms arg of LandsatPystacSearcher doesn't work with usgs landsatlook

[jessjaco]

The platform string is formatted differently than coded here:

dep-tools/dep_tools/searchers.py

Lines 147 to 150 in c377fe1

	if self._exclude_platforms is not None:
	landsat_platforms = ["landsat-5", "landsat-7", "landsat-8", "landsat-9"]
	query["platform"] = {
	"in": [p for p in landsat_platforms if p not in self._exclude_platforms]

It looks like it's LANDSAT_8, etc. See e.g https://landsatlook.usgs.gov/stac-server/collections/landsat-c2l2-sr/items/LC08_L2SR_076068_20201231_20210308_02_T2_SR

[jessjaco]

I supposed valid platforms could be read from the collection itself. See https://landsatlook.usgs.gov/stac-server/collections/landsat-c2l2-sr/ versus https://earth-search.aws.element84.com/v1/collections/landsat-c2-l2