Add default-authorization-mode feature flag

[creydr]

As the Eventing Authorization describes the feature track leverages a new config-features configuration called default-authorization-mode.

We should add:

• the new flag in https://github.com/knative/eventing/blob/main/config/core/configmaps/features.yaml with value allow-all
• the new flag name in https://github.com/knative/eventing/blob/main/pkg/apis/feature/flag_names.go
• The additional possible flag values: [allow-all, deny-all, allow-same-namespace] in

  eventing/pkg/apis/feature/features.go

  Lines 30 to 47 in 844dcbf

  	// Enabled turns on an optional behavior.
  	Enabled Flag = "Enabled"
  	// Disabled turns off an optional behavior.
  	Disabled Flag = "Disabled"
  	// Allowed neither explicitly disables or enables a behavior.
  	// eg. allow a client to control behavior with an annotation or allow a new value through validation.
  	Allowed Flag = "Allowed"
  	// Strict is only applicable to the TransportEncryption feature.
  	// The following applies:
  	// - Addressables must not accept events to non-HTTPS endpoints
  	// - Addressables must only advertise HTTPS endpoints
  	Strict Flag = "Strict"
  	// Permissive is only applicable to the TransportEncryption feature.
  	// The following applies:
  	// - Addressables should accept events at both HTTP and HTTPS endpoints
  	// - Addressables should advertise both HTTP and HTTPS endpoints
  	// - Producers should prefer to send events to HTTPS endpoints, if available
  	Permissive Flag = "Permissive"

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[pierDipi]

/assign