Support OPTIMADE filtering language #886
Description
We should expose an endpoint that allows OPTIMADE-esque search on all entries. I don't think we want to go quite as far as exposing a full OPTIMADE API (i.e., with info endpoints) -- at least not yet -- but using the OPTIMADE filter -> MongoDB query transformer (https://github.com/Materials-Consortia/optimade-python-tools/blob/main/optimade/filtertransformers/mongo.py) should be quite powerful. I might need to restructure optimade-python-tools upstream to allow for this part of the package to be installed without needing e.g. pydantic v2.