Retire deadLetterChannel, use DeliveryStatus consistently

[evankanderson]

Add DeliveryStatus to Channelable.

Fixes #5364

Proposed Changes

• 🎁 Add deadLetterSinkUri to make Channelables spec-compliant.
• 🧹 Start the deprecation clock ticking on deadLetterChannel.
• 🧹 Make DeliveryStatus actually used, as suggested in Remove v1.DeliveryStatus, which was unused outside of pkg/apis. #5745

Pre-review Checklist

• At least 80% unit test coverage
• [na] E2E tests for any new behavior
• [na] Docs PR for any user-facing impact
• [na] Spec PR for any new API feature
• [na] Conformance test for any change to the spec

Release Note

* Adds deadLetterSinkUri to the Channel status.
* Deprecates deadLetterChannel with a 1-year timer.

Docs

No docs needed; the only mention of deadLetterChannel is in the auto-generated docs.

[codecov]

Codecov Report

Merging #5746 (94c5642) into main (f031ba2) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #5746      +/-   ##
==========================================
- Coverage   82.65%   82.62%   -0.04%     
==========================================
  Files         202      202              
  Lines        6326     6314      -12     
==========================================
- Hits         5229     5217      -12     
  Misses        758      758              
  Partials      339      339              

Impacted Files	Coverage Δ
pkg/apis/duck/v1/channelable_types.go	97.95% <ø> (ø)
pkg/apis/duck/v1/delivery_types.go	91.66% <ø> (ø)
pkg/apis/duck/v1beta1/delivery_conversion.go	100.00% <ø> (ø)
pkg/apis/eventing/v1/broker_types.go	66.66% <ø> (ø)
pkg/apis/eventing/v1/trigger_types.go	100.00% <ø> (ø)
pkg/apis/messaging/v1/subscription_types.go	66.66% <ø> (ø)

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[lionelvillard]

@evankanderson do you want to get this in or add the fix you mentioned in Slack in this PR?

[evankanderson]

The other spec fix is in a completely different place for a different issue (Subscription's spec.subscriber being empty is permitted when we closed that in the spec).

This one is complete as is.

[lionelvillard]

/lgtm
/approve

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: evankanderson, lionelvillard

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