Changes to GET /v2/webhooks

added the new program_events/customer.challenge_completed enum value to the webhooks/items/topic response property for the response status 200

added the new program_events/customer.challenge_milestone_approaching enum value to the webhooks/items/topic response property for the response status 200

added the new program_events/customer.challenge_milestone_reached enum value to the webhooks/items/topic response property for the response status 200

added the optional property error/code to the response with the 401 status

added the optional property error/code to the response with the 403 status