add support for emitting webhooks

Microsoft Graph has types that are only used when the service calls to the client's APIs: change notifications.
In the Microsoft Graph pipeline, those types are being trimmed by kiota because they are not used anywhere (any inbound endpoint).
We should:

1. come up with an annotation that means "used for a webhook"
2. add this annotation to the metadata via XOD
3. leverage that annotation here so a webhook definition can be added to the description
4. have kiota project the types from webhooks components, and not trim them.

Empieza por rastrear la Microsoft Graph pipeline, el XOD metadata flow y el recorte que hace Kiota de los tipos que no utilizan los endpoints entrantes. Define cómo deben representarse y consumirse las anotaciones de webhook en la descripción generada. Se considera terminado cuando las definiciones de webhook conservan los tipos necesarios y Kiota los proyecta en lugar de recortarlos.