When threshold value is set, knn plugin will not be creating graph.
Hence, when search request is trigged during that time, exact search
will return valid results. However, radial search was never included
as part of exact search. This will break radial search when threshold
is added and radial search is requested. In this commit, new method
is introduced to accept min score and return documents that are greater
than min score, similar to how radial search is performed by native
engines. This search is independent of engine, but, radial search is
supported only for FAISS engine out of all native engines.

Signed-off-by: Vijayan Balasubramanian <[email protected]>

Signed-off-by: Vijayan Balasubramanian <[email protected]>

Signed-off-by: Vijayan Balasubramanian <[email protected]>