load-balancing

[Semior001]

allow user to introduce several upstreams for a match, e.g.:

  - match:
      uri: "com.github.Semior001.groxy.example.mock..Upstream/Get"
    forward:
      upstreams:
        - example-1
        - example-1-replica
      load-balancing: round-robin

remove the "upstream" field from the config, consumers now must specify a list of upstreams, optionally setting the load balancing policy, default is round-robin