List available webhook event types

Returns all event types that can be subscribed to. Includes session events (e.g. `session.approved`, `session.declined`, `session.resubmission-required`) and identity events (`identity.created`, `identity.updated`, `identity.archived`, `identity.restored`, `identity.tag-added`, `identity.tag-removed`). The `session.resubmission-required` event fires when a session is auto-rejected because the submitted ID photos were too blurry or low-quality for OCR processing. The applicant must create a new session with the same `external_ref` and resubmit clearer photos.