E2E test that verifies popular Helm charts deployment

[alexmt]

Summary

Popular off the shelf Helm charts contain a lot of edge cases related to resource diffing. The automated test that deploys such charts and ensures that Argo CD don't report any unexpected differences should help to catch bugs early and improve Argo CD quality.

Proposal

• Implement E2E using framework in https://github.com/argoproj/argo-cd/tree/master/test/e2e
• Test potentially can be very time consuming, so it should be possible to run it separately from main e2e test suite
• It is proposed to deploy latest version of the following helm charts:
  • Cert-manager https://hub.helm.sh/charts/jetstack/cert-manager
  • Prometheus https://github.com/prometheus-community/helm-charts
  • External DNS: https://github.com/bitnami/charts/

[wtam2018]

@alexmt Please assign to @wtam2018