Leverage `network.GetServiceHostname`
Leverage `network.GetServiceHostname`

Today triggers hard-codes `.svc.cluster.local`, but `cluster.local` is actually configurable, so this will break on certain clusters.

Knative has a helper function that looks up the appropriate suffix for the cluster and simply uses that.

Ref: https://github.com/knative/pkg/blob/3a2ae6db70971afbcaf1e1c3826cbc9a5d6c718e/network/domain.go#L40

tektoncd/triggers,tektoncd/triggers