Load balancing simulation and visualization

It is often challenging to fully grok the interaction of Envoy's sophisticated load balancing schemes, priorities, localities, failover, overprovisioning, health, panic mode, etc. We have some documentation describing this at https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/upstream/load_balancing/load_balancing, but there is still a significant gap between this and truly understanding e2e the resulting LB behavior from a given configuration.

I think some tooling here would be quite amazing. Two ideas:

1. A CLI tool that takes a `Cluster` configuration, as well as endpoint health and registration status (e.g. in a `ClusterLoadAssignment`) and produces a distribution of expected traffic across endpoints.

2. A web UX similar to (1) that allows the visual construction of the LB topology and other inputs. This would then be able to use some sort of visual representation of load distributions across hosts (even just proportionally sized circles would be neat as a starting point). As a bonus, the real Envoy LB implementation could be used in the browser via WebAsm and fakes/mocks.

This is not high priority but would be an amazing documentation and user education feature for someone with the right skillset for (1) and (2).