Implement webhook client (repository layer)

[aldy505]

It should:

• Create a constructor that set the target URL
• Do an exponential backoff for failed request (response status code of 5xx or context deadline exceeded)
• Parse the StatusUpdate struct into JSON string. You can put additional JSON annotation there.

mock-shipping-provider/repository/webhook_client.go

Lines 10 to 28 in 68058d6

	type WebhookClient interface {
	// SendStatusUpdate should send a POST request to the destination target URL (configured somewhere else)
	// with the JSON request body of:
	//
	// {
	// "reference_number": "string",
	// "air_waybill": "string",
	// "status_code": 3,
	// "status_description": "IN_TRANSIT",
	// "timestamp": "time.RFC3339",
	// "note": "string"
	// }
	//
	// It should do a retry with exponential backoff if the client returns 500 status code,
	// or a timeout error happened.
	//
	// If the response status code is 400, it should throw an error and don't continue.
	SendStatusUpdate(context.Context, StatusUpdate) error
	}