Delivery Format: set kn-ingress-format ce extension in receiver

[Cali0707]

Problem
To support dispatching events from the Kafka based eventing components with the correct format when a user sets the spec.delivery.format to ingress, we need to set a cloudevent extension of kn-ingress-format to specify which format was used. This should be set to structured if the input event was structured, and binary if the input event was in binary. However, since this event may have been forwarded from earlier ingress, we need to only set the kn-ingress-format extension if it is not already present on the event.

Persona:
Which persona is this feature for?

Exit Criteria
Unit tests verifying that:

1. If the extension is not present it is set correctly for both structured and binary events
2. If the extension is already present, it is not changed for both structured and binary events

Time Estimate (optional):
How many developer-days do you think this may take to resolve? 1-2

Additional context (optional)
Add any other context about the feature request here.

• Parent issue: Delivery Format: support specifying the event format knative/eventing#8057

[Cali0707]

/help

[knative-prow]

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[Cali0707]

/triage accepted

[Cali0707]

Given changes to the design of the feature, this is no longer needed