Delivery Format: support specifying the event format

**Problem**
Currently, when dispatching an event, we generally send it in the binary event format. However, to integrate with some systems (such as AWS EventBridge) we will need to be able to support sending events in structured format.

To support this, we are going to add a new field to the `Delivery` spec of resources, which will look like:

```yaml
spec:
delivery:
format: ingress|structured|binary|null
```
If set to `binary`, then the component would deliver the event in binary format. If set to `structured`, then the component would deliver the event in structured format. If set to `ingress`, then the component would send the event in the format that the broker received it.

**[Persona:](https://github.com/knative/eventing/blob/main/docs/personas.md)**
Which persona is this feature for?
System integrators

**Exit Criteria**
An e2e test for each resource that supports the delivery spec that verifies that the event was received in structured format.

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

**Additional context (optional)**