When you create a new product, set it to Istio integration and try to update the configuration it won't work and will return Unable to update the staging configuration.

DEV NOTES:

The problem seems to be that the product doesn't have an associated backend. The first product has always a backend by default, so we have to create a second one in order to reproduce this. Since an istio product doesn't have the section "Integration > Backends" visible it is not easy to guess what's the error about. We can just re-enabled this section in the vertical navigation and let the user add a backend api.

Remove backend_api requirement (model validation) for Istio products.

WORKAROUND:

Change the product back to no-istio, set a backend, change to istio again, update config -> it should pass.