Integration with (external) cert-manager

How to integrate cert-manager with OSSM:

• Customer want to use cert-manager as an issuer
• they wont use the self-signed certificates that the mesh uses by default
• We need a own certificate provider that generates certificate
  so cu configured in this way

  certificateAuthority:
    type: Custom
    custom:
      address: cert-manager-istio-csr.cert-manager.svc:443
  

• However, istiod still uses a self-signed certificated for the communication from gateway – virtual-service.
• They want istio itself also request a certificate from cert-manager.
  However, the customer achieved the integration but wants to here from engineer side best and possible way.....
• IBM P/Z platforms are not supported by the Cert-Manager Operator.