Add timeout and retries

[stefanprodan]

This PR adds HTTP timeout and retries as optional fields to the Canary service spec.

  service:
    # container port
    port: 9898
    # Istio gateways (optional)
    gateways:
    - public-gateway.istio-system.svc.cluster.local
    # Istio virtual service host names (optional)
    hosts:
    - podinfo.example.com
    # HTTP match conditions (optional)
    match:
      - uri:
          prefix: /
    # HTTP rewrite (optional)
    rewrite:
      uri: /
    # timeout for HTTP requests (optional)
    timeout: 5s
    # retry policy when a HTTP request fails (optional)
    retries:
      attempts: 3

Fix #61

[codecov-io]

Codecov Report

Merging #62 into master will increase coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #62      +/-   ##
==========================================
+ Coverage   55.45%   55.57%   +0.12%     
==========================================
  Files           9        9              
  Lines        1385     1389       +4     
==========================================
+ Hits          768      772       +4     
  Misses        481      481              
  Partials      136      136

Impacted Files	Coverage Δ
pkg/controller/router.go	85.64% <100%> (+0.27%)	⬆️

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