Provide a way to query for the instance assignment for a given trace ID

[kentquirk]

Is your feature request related to a problem? Please describe.

One way to reduce or eliminate refinery-to-refinery span traffic would be to allow a smart load balancer to distribute traces to the "correct" refinery. But the distribution algorithm is complex and not easily recreated by an outside service.

Describe the solution you'd like

A query endpoint that a load balancer could use to find out which node should receive a given trace.

Either:

• Built into Refinery directly
• A separate executable that could be run as a local service (it would have to be listening to the peer gossip conversation to keep up to date with the current state of the nodes)

Describe alternatives you've considered

If Refinery nodes aren't clustered, they won't talk to each other. A smart load balancer could make its own decisions with its choice of algorithm without affecting how Refinery behaves.

Additional context
Pollinators discussion