Remove strict subscriber feature flag

[creydr]

Fixes #5756

As per knative/specs#30 the spec was changed from requiring one of spec.subscriber or spec.reply to be set to require that spec.subscriber is set.

As part of this change the strict-subscriber feature flag was introduced to disable this validation (#5762) and promoted to beta (enabled by default) in 1.7 (#6473).

🧹 This commit removes this feature flag again so the validation can't be disabled anymore.

Proposed Changes

• Remove strict-subscriber feature flag
• Promote strict subscriber validation to GA

Pre-review Checklist

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

Release Note

Remove the possibility to disable strict subscriber validation.
When the reply field is specified without a subscriber, the reply field won't be used as a subscriber by default and the subscriber validation will fail.

[knative-prow]

Hi @creydr. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[codecov]

Codecov Report

Base: 81.94% // Head: 81.90% // Decreases project coverage by -0.04% ⚠️

Coverage data is based on head (95c7a3c) compared to base (82bf83c).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6608      +/-   ##
==========================================
- Coverage   81.94%   81.90%   -0.05%     
==========================================
  Files         235      235              
  Lines       11774    11763      -11     
==========================================
- Hits         9648     9634      -14     
- Misses       1650     1653       +3     
  Partials      476      476              

Impacted Files	Coverage Δ
pkg/apis/messaging/v1/subscription_validation.go	87.71% <100.00%> (-1.99%)	⬇️
pkg/reconciler/subscription/subscription.go	83.33% <0.00%> (-0.80%)	⬇️

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[pierDipi]

/ok-to-test

[pierDipi]

/lgtm

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: creydr, pierDipi

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• OWNERS [pierDipi]

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[matzew]

@creydr Wanna follow up on this: https://github.com/knative/docs/blob/main/docs/eventing/experimental-features/strict-subscriber.md

[creydr]

@creydr Wanna follow up on this: https://github.com/knative/docs/blob/main/docs/eventing/experimental-features/strict-subscriber.md

👍
knative/docs#5332