queue: remove MetricsRegistry static instance

If the host app has multiple queues, this makes it easier to let it
manage the metrics as part of its lifecycle.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
queue: namespace bus options

This is useful to configure the external bus differently in Kill Bill
for example.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>