kumo.on('get_egress_path_config', function(domain, egress_source, site_name))
This event handler is in flux and may change significantly
Not the final form of this API, but this is currently how we retrieve configuration used when making outbound connections
routing_domain parameter corresponds to the effective
routing_domain of the
originating scheduled queue. This will be the same as the recipient domain
unless the message had set the
routing_domain meta value.
See also kumo.make_egress_path.