Add pgstac (moved from stac-utils/pgstac) #619

Job	Run time
test-ubuntu-with-pgstac	31s
test-ubuntu-with-gdal	2m 11s
doc	1m 13s
build	1m 2s
fmt	6s
test-macos	45s
test-ubuntu (-p stac)	22s
test-windows	3m 44s
test-ubuntu (-p stac -F reqwest)	1m 12s
test-ubuntu (-p stac-api)	13s
test-ubuntu (-p stac -p stac-api -F geo)	34s
test-ubuntu (-p stac-async)	42s
test-ubuntu (-p stac-cli --no-default-features)	1m 8s
test-ubuntu (-p stac-validate)	1m 1s
	14m 44s

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