/kind bug

What steps did you take and what happened:
Installing the Katib manifests in K8s 1.16 makes the cert-generator script fail with:

error: error validating "STDIN": error validating data: ValidationError(CertificateSigningRequest.spec): unknown field "signerName" in io.k8s.api.certificates.v1beta1.CertificateSigningRequestSpec; if you choose to ignore these errors, turn validation off with --validate=false

This is a client-side validation error because the CertificateSigningRequest API does not contain the signerName field in 1.16 (needs >= 1.18). @andreyvelich tried the script with --validate=false in 1.16 KIND and it worked. We also tried it with a cert-manager Certificate and it worked.

Next Steps:

• Add --validate=false to cert-generator script
• Add a katib-with-kubeflow-cert-manager overlay, which uses cert-manager to create the Certificate