eventing: Trigger deadLetterUri does not conform to specification, should be deadLetterSinkUri

Describe the bug A clear and concise description of what the bug is.

In Trigger Lifecycle specification, it specify the following:

If the Trigger's `spec.delivery.deadLetterSink` field it set, it MUST be resolved to a URI and reported in `status.deadLetterSinkUri` in the same manner as the `spec.subscriber` field before setting the Ready condition to true.

The newly merged new feature https://github.com/knative/eventing/pull/5551 does not conform to this specification.

Additionally, since the CRD for Broker and Trigger does not contain deadLetterSinkUri nor deadLetterUri in status field, this change actually did not do anything as the newly added deadLetterUri is removed anyway.

Expected behavior A clear and concise description of what you expected to happen.

• Status for resolved dead letter sink URI correctly conforms to specification (use deadLetterSinkUri instead of deadLetterUri)
• CRD for Broker and Trigger contains deadLetterSinkUri in status

To Reproduce Steps to reproduce the behavior.

1. Install Knative Eventing 0.25, MTChannelBasedBroker 0.25 and InMemoryChannel 0.25
2. Create a trigger with deadLetterSink delivery option
3. Trigger is resolved without deadLetterUri
4. Manually add deadLetterUri to Trigger CRD
5. Trigger is resolved with deadLetterUri

Knative release version

0.25

Additional context Add any other context about the problem here such as proposed priority