Introduce CRD v1: fix CRD generation bugs and enable field validation

[elanv]

This PR introduces CRD v1.
CRD v1 is supported in Kubernetes version 1.16+.

• Note
  There is a known issue(Restricted CRD API group "k8s.io" #382) for introducing CRD v1. For now, applied a workaround marking the CRD annotation api-approved.kubernetes.io as unapproved. Unapproved domain use is still a remaning issue.

• Descrition

  • Fix CRD generation bugs (fix Kubernetes V1.18 support for CRD #311, fix make deploy failed: The CustomResourceDefinition "flinkclusters.flinkoperator.k8s.io" is invalid #266, fix Not able to deploy the Operator with master branch code #330, fix flink-cluster-crd.yaml #406, )
  • Reject unknown fields (fix Reject unknown fields in the CR #85)
  • Introduce CRD validation (via kubebuilder markers)
    Now can use kubebuilder validation markers that can partially replace the functions of default/validating webhooks and their test codes.
    https://book.kubebuilder.io/reference/markers/crd-validation.html

[jlewi]

Thanks for the fix!

@functicons @hongyegong Is there anything blocking merging this PR? Looks like the tests are blocked on someone approving the tests to run?