design: what is the right abstraction for a bridge

menshen agent was designed to report the congestion of the openvpn gateways. it gathers statistics and reports to the menshen coordinator.

if we're going to abstract it for bridges, we need to decide what is the metric being reported:

• openvpn "fullness" cannot be reported for fully encrypted transports (we might want to derive a similar metric to count the number of simultaneus connections being served).
• reporting load for the bridge alone doesn't serve the original purpose of avoiding congestion on the destination gateway.

this makes me think that we need to inform menshen of what is the sink of the bridges traffic, to combine the statistics from the bridge and the destination gateway in a meaningful way.

the location (egress ip) is also needed for the ux (although the ingress location for the bridge might also be relevant). we might want to report this info dynamically.