Delivery Format: support specifying the event format in the kncloudevents dispatcher

[Cali0707]

Problem
Throughout eventing, we use the kncloudevents dispatcher to dispatch cloudevents. We should add a SendOption which allows us to specify the format used when sending the events, along the lines of:

dispatcher.SendEvent(ctx, event, destination, WithEventFormat(format.Structured))

When no event format is specified, we should preserve the existing behavior of the package.

Persona:
Which persona is this feature for?

Exit Criteria
A unit test which sends an even with the structured format set and verifies that it gets a structured event, and a unit test which does the same for the binary format

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: add the format field to the Delivery type #8073
• kncloudevents dispatcher code: https://github.com/knative/eventing/blob/main/pkg/kncloudevents/event_dispatcher.go
• To force binary or structured encoding, https://github.com/cloudevents/sdk-go/blob/8efefb01754a924e4c33e0d50b673fc1ee18815f/v2/binding/write.go#L125-L133 can be used

[Cali0707]

/good-first-issue

[knative-prow]

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[EraKin575]

/assign