properly evaluate property filters

[bossie]

openeo_driver.filter_properties.extract_literal_match does not actually evaluate the callback/predicate process graphs in the properties argument to load_collection/load_stac; rather, it handles the JSON in a more mechanical way so it only works for the simplest of cases.

Evaluating these predicates against properties of features (client-side filtering) seems doable and intuitive but instead we typically translate them to HTTP params (server-side filtering).