Do not alter database entries when running tests

[vincentsarago]

When running pcstac tests, we assume

planetary-computer-apis/scripts/setup

Lines 30 to 34 in f2cff0d

	docker-compose \
	-f docker-compose.yml \
	run --rm \
	stac \
	python /opt/src/pcstac/tests/loadtestdata.py

has being ran first.

This could be replaced by something like: https://github.com/developmentseed/planetary-computer-apis/blob/refactorTests/pcstac/tests/conftest.py#L19-L115

Note: ☝️ approach also remove the code duplication with pcstac.main

This is also linked to #31 because loadtestdata.py assume pypgstac is available in the environment (which should only be in the dev environment)