Structs for webhook payloads

[aidansteele]

It would be quite useful if there were structs that corresponded to webhook events, e.g. like dsync.user.updated.

For the above example, there is the directorysync.User type but it's not quite right. Compare its definition https://github.com/workos-inc/workos-go/blob/83f29941b8a27e7693d229c4ce9190bf581a47f2/pkg/directorysync/client.go#L57-L75

To the payload definition:

(The directory_id field is missing)