feature request: advanced load balancing

[justrp]

Current load balancing is using round robin strategy. I'd like to have more intelligent balancing strategies:

• weights-based
• latency-based (technically, it might be somehow implemented via weights controlled by external infrastructure)
• tokens capacity/demand based (different endpoints might have different capacity - but that also might be solved by weights-based)

Some alternative solutions already claim to have this (e.g. https://github.com/microsoft/AICentral)