Document trigger.spec.subscriber type and usage with a particular path

[pierDipi]

In this page https://knative.dev/development/eventing/triggers/ we don't explain how
to send events to Trigger's subscriber to a particular path using spec.subscriber.uri
or a combination of spec.subscriber.ref and spec.subscriber.uri.

Additional Info

• https://pkg.go.dev/knative.dev/pkg/apis/duck/v1?tab=doc#Destination

[pierDipi]

/assign