* v2: add documentation for circuit breaker config and "random selection" load balancing policy
* v2: rename circuit breaker config inline key from `type` to `breaker` to avoid json key clash between the `circuit_breaker` type and the `type` field of the generic circuit breaker Config struct used by circuit breaking implementations
* v2: restore the circuit breaker inline key to `type` and rename the name circuit breaker config field from `Type` to `Factor`