Allow users to specify a suffix for `--advertise-host` argument

As found [here](https://github.com/cockroachdb/cockroach-operator/blob/c133bd007e0ee9e6a0bc25f408943c5200188b71/pkg/resource/statefulset.go#L361-L362) the `--advertise-host` argument is built based on the pod name, and the namespace. In our instance our nodes exist in different Kubernetes clusters, but have the same podnames and namespace. What makes our nodes uniquely identifiable is their FQDN (what cluster they're in).

I know it's not supported but would it make sense to have an option to specify a suffix for these names?

So the code would look something like
```go
suffix := ""
if b.Spec().AdvertiseSuffix != nil {
suffix = fmt.Sprintf(".%s", *b.Spec().AdvertiseSuffix)
}

...
fmt.Sprintf("--advertise-host=$(POD_NAME).%s.%s",
b.Cluster.DiscoveryServiceName(), b.Cluster.Namespace(), suffix)
```

Or something of the sort.