Update an entity in a preview session

Updates an experience, experience fragment, component, experience template, or data assembly. Set `sys.id` to the entity ID and `sys.type` to select the corresponding request shape. Send the complete entity configuration, not a partial patch. Other `sys` fields are managed by the service. Use the same Content Management API token that created the session. Updates with another token return `403`, even if that token has permission to update preview sessions. Subscribers receive the latest preview state. Rapid edits may be combined into one update. If authorization or a required service is temporarily unavailable, the request returns `503`.