Update Outbound Shipping Method of Exchange

Add Outbound Shipping Method to Exchange POST

Add an outbound shipping method to an exchange. The outbound shipping method will have a `SHIPPING_ADD` action.

Remove Outbound Shipping Method from Exchange DELETE

Remove the shipping method for delivering outbound items in the exchange using the `ID` of the method's `SHIPPING_ADD` action. Every shipping method has an `actions` property, whose value is an array of actions. You can check the action's name using its `action` property, and use the value of the `id` property.