Avoid fatal errors for unknown features flags that can be added in a future release

[pierDipi]

Once backported fixes Upgrade test failures like https://prow.knative.dev/view/gcs/knative-prow/logs/continuous_eventing_main_periodic/1806130105928388608

Error initializing feature-flags config \"config-features\": \"cannot parse the feature flag 'default-authorization-mode' = 'allow-same-namespace'\"

Proposed Changes

• Avoid fatal errors for unknown features flags that can be added in a future release

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

Docs

[pierDipi]

/cherry-pick release-1.14

[knative-prow-robot]

@pierDipi: once the present PR merges, I will cherry-pick it on top of release-1.14 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.14

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-sigs/prow repository.

[Cali0707]

/lgtm

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Cali0707, pierDipi

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Needs approval from an approver in each of these files:

• OWNERS [Cali0707,pierDipi]

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 67.69%. Comparing base (a6ac811) to head (5a9ecfc).

Files	Patch %	Lines
pkg/apis/feature/features.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8051      +/-   ##
==========================================
- Coverage   67.70%   67.69%   -0.01%     
==========================================
  Files         364      364              
  Lines       17042    17043       +1     
==========================================
  Hits        11538    11538              
- Misses       4783     4784       +1     
  Partials      721      721              

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[knative-prow-robot]

@pierDipi: new pull request created: #8052

In response to this:

/cherry-pick release-1.14

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-sigs/prow repository.