YARP to combine with load balancing

[VenkateshSrini]

What should we add or change to make your life better?

I would like YARP to add a Load balancing facility. It can be thought of in two format

1. One is Canary deployment, where we can say we need 80% traffic to the old route and 20% to the new one.
2. Unirfomly distribute load using round-robin method across routes

Why is this important to you?

1. In Kubernetes deployment we can use this easily. Otherwise, just for such a small requirement, we need to install cluster wide service mesh. As we all understand Service Mesh is complex.

[Tratcher]

1. One is Canary deployment, where we can say we need 80% traffic to the old route and 20% to the new one.

This is tracked under A/B testing at #126

2. Unirfomly distribute load using round-robin method across routes

Load balancing is enabled by default, and round-robin is one of the options. The default load balancing algorithm is PowerOfTwoChoices since it is both very quick and simple but still quite good at distributing load. Round-robin assumes all requests are of equal cost, it doesn't take into account any backlog that builds up on a given node.

reverse-proxy/src/ReverseProxy/Service/LoadBalancing/PowerOfTwoChoicesLoadBalancingPolicy.cs

Lines 30 to 31 in 58da96a

	// Pick two, and then return the least busy. This avoids the effort of searching the whole list, but
	// still avoids overloading a single destination.

[karelz]

Duplicate of #126