Modify "Processing Time" of the shipping service #118
Description
We need to extend the ShippingService, written in Go, to allow setting the processing time.
- introduce JWT authentication and authorization to the service
- introduce a new endpoint where that lets the caller set a range from which a random processing time will be picked during shipping
- This new endpoint must only be called by authenticated users with the "admin" scope
This issue corresponds to Task 1 in #84.