Improve filtering on getList

I see two alternative implementations which could be explored:

• delegate rql generation of restrictions to the GUI (could be comined with helper methods). The filters received by getList would be in the form {"restrictions": ["X city ~= '%ac'", "X start_date > "2020-10-10"]} It could be implemented using parse/format on the inputs.
• pass the filtering strategy as a parameter of createDataProvider. (filter, {resource, schema}) => RqlRestriction[]

Maybe the way facets are implemented in Cubicweb could be inspiring.