add support for multiple httpproxies

[sneako]

Closes #19

[sneako]

Attached are the logs for a rollout performed in a local kind cluster with two httpproxies pointed at a single service with the following strategy:

  strategy:
    canary:
      canaryMetadata:
        labels:
          rollout: canary
      canaryService: httpbin-canary
      dynamicStableScale: true
      maxUnavailable: 1
      stableMetadata:
        labels:
          rollout: stable
      stableService: httpbin
      steps:
      - setWeight: 10
      - pause:
          duration: 10
      - setWeight: 30
      - pause:
          duration: 10
      - setWeight: 50
      - pause:
          duration: 10
      - setWeight: 100
      trafficRouting:
        plugins:
          argoproj-labs/contour:
            httpProxies:
            - httpbin
            - httpbin-2
            namespace: default

rollout.txt

[izturn]

LGTM thx