feat: ingest FeatureContextConstraint-based catvars

[jsstevenson]

• Enable DB ingest of CDM files containing FeatureContextConstraint-based catvars (this is not possible yet on the current staging branch but can be produced by the code in feat: add '<gene> mutation' catvars from MOA #651)
• Enable retrieval of statements with FeatureContextConstraint-based subjects by the non-variant properties. EG, if a statement proposition consists of (crudely) {subjectVariation="IDH1 mutation", geneContext="IDH1", objectCondition="low-grade glioma"}, then searching by gene=IDH1 or disease=low-grade glioma would be able to return this statement along with any other relevant statements. Note that this does NOT implement retrieval by variation -- I've made a separate discussion to work out desired behavior there.
• As far as I can tell, this... just works on the frontend already, since this doesn't change the schema (just uses some more of the existing schema). eg