config: Require named list filter lookups to use settings_filter_name

config: Require named list filter lookups to use settings_filter_name

The config client callers are now responsible for doing lookups with e.g.
settings_filter_name=namespace/inbox in the event, rather than relying on
just namespace=inbox being in the event.

This allows separating the filter name from the setting values. So for
example userdb can change the mailbox name (mailbox/spam/name=Junk).