This introduced a new knn query:
- knn query is executed during the Query phase similar to all other queries.
- No k parameter, k defaults to size
- num_candidates is a size of queue for candidates to consider while
search a graph on each shard
- For aggregations: "size" results are collected with total = size * shards.
Aggregations will see size * shards results.
- All filters from DSL are applied as post-filters, except: 1) alias filter
is applied as pre-filter or 2) a filter provided as a parameter
inside knn query.
