`generic_worker` should support requests to `/_matrix/client/v3/directory/room/{roomAlias}`

[richvdh]

Currently, /_matrix/client/v3/directory/room/{roomAlias} has to be routed to the main process, which is a bit silly because these can be relatively high volume, and handling them on the main process means they are handled more slowly than necessary.

I don't think there are any particular problems with handling this on a worker process.