Delivery format: add and provision format field to EgressConfig in contract

[Cali0707]

Problem
To support dispatching events in the format specified in the format field being added into the delivery spec of components, we need to add a field into the contract, and then provision that field from the control plane.

Persona:
Which persona is this feature for?

Exit Criteria
Unit tests indicating that the reconciler is setting the contract properly

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
• Required before this can be worked on: Delivery Format: add the format field to the Delivery type knative/eventing#8073

[Cali0707]

/help

[knative-prow]

@Cali0707:
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In response to this:

/help

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[Cali0707]

/assign

[github-actions]

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