Feature request: limit nodes hit by "serverSideEmit" and "fetchSockets" in sharded adapter

[cody-evaluate]

In the redis sharded adapter, you should be able to optionally specify a channel name to emit "serverSideEmit" or "fetchSockets" to limit network activity in some cases where you know where the event needs to go that way not every subscriber gets the event.

In some cases I know the name of a specific channel a socket.io server is subscribed to. The ability to call "serverSideEmit" or "fetchSockets" with an explicit channel name (per request) would be awesome.