If `istio.ingress.*` is not defined, Big Bang Helm Release will return an error due to ingress.key set to nil

In the template, if istio.ingress.key and istio.ingress.cert are not included in one of the secrets or configmaps, the Helm Release will fail with template: bigbang/templates/istio/controlplane/secret-tls.yaml:1:46: executing "bigbang/templates/istio/controlplane/secret-tls.yaml" at <.Values.istio.ingress.key>: nil pointer evaluating interface {}.key

To workaround this issue, set the following in one of the secrets/configmaps:

istio:
  ingress:
    key: ""
    cert: ""

If you are passing your TLS certs inline, add the cert into the value. Otherwise, if you are creating your cert outside of Big Bang, create an empty string.