Allow to finish a subscription line before it's next consumption
We've got the following case:
1. One customer has a running subscription service (which has been already invoiced)
2. Before the next consumption the customer wants to upgrade to a different service.
In order to do so we want to set the end date for the line to the day before the next subscription and we create a new line with the new service. But when trying to do so the server complains that the end date must be higher than the next_consumption date.
I think we should allow to end the line before next consumption and do not create the next consumption as the service have never consumed.