As of `v0.9.0` Vero [requires a network to be specified as a CLI
argument](https://github.com/serenita-org/vero/releases/tag/v0.9.0).
This PR adds that to the Kurtosis definition for the Vero VC service.

(In case you're wondering - how did Vero not have a `--network` flag
before? It used to load all the spec values from the connected beacon
node(s) and would then dynamically create all necessary SSZ classes.)

I tested this manually with the `.github/tests/vero-all.yaml` config and
have been using this version for the last few months while preparing for
Pectra.