Add e2e testing

[slopezz]

• Adds basic e2e tests with kind and kttl
• make target test-e2e will:
  • Download specific kind binary to local bin/ directory (if not exists)
  • Download specific kuttl binary to local bin/ directory (if not exists)
  • Create a kind cluster
  • Build operator image locally, and load it into the kind cluster
  • Deploy the operator with previous built image using official make deploy target but using config/testing kustomize (for example, it will create prometheus ServiceMonitor and GrafanaDashboard CRDs which are not present on the kind cluster by default)
  • Execute a couple of tests against the deployed operator on the kind cluster
  • Test: operator: checks that operator Deployment has 1 ready replica, and that expected Role, RoleBinding and ServiceAccunt objects have been created
  • Test: prometheusexporter: deploy example-memcached PrometheusExporter, and check that operator creates its dependant objects (Deploymentwith 1 ready replica, Service, ServiceMonitor and GrafanaDashboard)

[raelga]

Great job!

/lgtm

[slopezz]

/assign

[raelga]

/lgtm

[slopezz]

/approve

[3scale-robot]

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