in grpc:
- restructure `ContextInput`, so that it becomes easy to handle both pairs and positive/negative lists in the future
in rest:
- restructure context queries so that they don't repeat the label in order to be used . E.g. turn `{ query: { context: { context: [ ... ] } } }` into `{ query: { context: [ ... ] } }`
- fixes fusion so that `{query: { fusion: "rrf" } }` actually works
both:
- renames `RecommendInput` positives and negatives to singular (same as in reco api)
8dc1eb235b