Missing CQL2_JSON conformance class

[jonhealy1]

Missing the CQL2_JSON conformance class. This should be added to stac-fastapi: https://github.com/stac-utils/stac-fastapi/blob/925a9bbc686dcb1f17808719ab9863c08b92ea36/stac_fastapi/extensions/stac_fastapi/extensions/core/filter/filter.py#L73-L81