Update the hybrid backend to limit its partition response to the requested channel set
requested to merge jonathan-hanks/arrakis-server:issue19_hybrid_backend_too_many_channels_in_response into main
- Previously if the channel list changed partitioning information would be sent back for all channels in the backend.
- Update the hybrid backend to limit the response to the set of channels sent in for this partitioning request.
Closes #19 (closed)