AWS App Mesh integration

[stefanprodan]

Add suport for AWS EKS App Mesh

• create/update App Mesh virtual nodes and virtual services
• implement canary rollout with progressive traffic weight (App Mesh has no A/B testing support)
• implement HTTP success rate metric check based on Envoy stats
• add service mesh provider flag -mesh-provider=appmesh

Example:

apiVersion: flagger.app/v1alpha3
kind: Canary
metadata:
  name: frontend
spec:
  targetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: frontend
  service:
    port: 9898
    # App Mesh reference
    meshName: global.appmesh-system
  canaryAnalysis:
    interval: 10s
    threshold: 10
    maxWeight: 50
    stepWeight: 5
    # App Mesh Prometheus checks
    metrics:
    - name: envoy_cluster_upstream_rq
      # minimum req success rate (non 5xx responses)
      # percentage (0-100)
      threshold: 99
      interval: 1m

Test infra: https://github.com/stefanprodan/appmesh-eks
Fix: #97

[codecov-io]

Codecov Report

Merging #107 into master will increase coverage by 0.77%.
The diff coverage is 61.69%.

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
+ Coverage   56.57%   57.34%   +0.77%     
==========================================
  Files          16       17       +1     
  Lines        1810     2049     +239     
==========================================
+ Hits         1024     1175     +151     
- Misses        627      698      +71     
- Partials      159      176      +17

Impacted Files	Coverage Δ
pkg/controller/observer.go	43.83% <0%> (-9.5%)	⬇️
pkg/router/factory.go	0% <0%> (ø)	⬆️
pkg/controller/controller.go	6.96% <0%> (-0.05%)	⬇️
pkg/controller/scheduler.go	37.61% <12.5%> (-2.02%)	⬇️
pkg/controller/deployer.go	59.11% <50%> (+0.66%)	⬆️
pkg/router/appmesh.go	78.01% <78.01%> (ø)

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