Add Webhooks model APIs

[Azquelt]

• add OpenAPI.webhooks
• add TCKs using model reader and static file
• add @Webhook annotation and @OpenAPIDefinition.webhooks
• add TCKs using the @Webhook annotation

For #583

[Azquelt]

Realised that @Webhook should be added to the list of annotations in the spec as well. I'll do this in another PR so that it doesn't conflict with #607

[Azquelt]

I've now updated the list of annotations in the spec.

[Azquelt]

Rebased on main

[MikeEdgar]

Should this also include parameters (applicable to all operations) and servers [1] since this is effectively a path item? I wonder also if it should have a $ref for the same reason.

[1] https://spec.openapis.org/oas/v3.1.0.html#fixed-fields-6

[Azquelt]

Should this also include parameters and servers

It could, but I'm not sure whether we should or not. Path items appear in four places: under paths, callbacks, webhooks and components (not yet added).

By far the most common is under paths and we don't currently have any way to add parameters or servers there with annotations since there's nothing in Jakarta REST that really maps to path item and so there's nowhere to put an annotation.

@Callback also represents a path item, so if we were to add parameters and servers to @Webhook, we should probably add them to @Callback as well.

I wonder also if it should have a $ref for the same reason.

Yes possibly. I was going to think about that under #437.

---

Another thought occurred to me: if we were to add a new annotation for #437, it would probably have identical fields to @Webhook (since both represent one entry in a Map<String, PathItem>). We could use one annotation (named @PathItem) for both instead.

[Azquelt]

Let's design this alongside #437.

I'll remove the annotations from this PR so we can get the model parts merged.

[Azquelt]

Annotations removed.

[MikeEdgar]

Looks good