[release-0.26] Default dead letter sink namespace to the object namespace

[knative-prow-robot]

This is an automated cherry-pick of #5748

The field `spec.delivery.deadLetterSink.ref.namespace` for Broker, Trigger, Channel and Subscription if not specified is defaulted to `metadata.namespace`.

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: knative-prow-robot, pierDipi

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [pierDipi]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-0.26@27dbb99). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff               @@
##             release-0.26    #5904   +/-   ##
===============================================
  Coverage                ?   82.68%           
===============================================
  Files                   ?      203           
  Lines                   ?     6346           
  Branches                ?        0           
===============================================
  Hits                    ?     5247           
  Misses                  ?      759           
  Partials                ?      340           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 27dbb99...e00b6bb. Read the comment docs.

[knative-prow-robot]

@knative-prow-robot: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-knative-eventing-build-tests	e00b6bb	link	true	/test pull-knative-eventing-build-tests

Full PR test history. Your PR dashboard.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[pierDipi]

broken due to Go 1.17: see #5906