fix: change how a form is saved as draft

[FredrikMWold]

The user should be able to save an unfinished form as a draft.

This functionality already exist in the backend but the api endpoints need work.
When a form is saved as a draft it uses the endpoint https://chemdec-dev.azurewebsites.net/api/shipment/offshore/change
Which is the same endpoint that is used to update an existing form.
Need a separate endpoint or a flag to set in the https://chemdec-dev.azurewebsites.net/api/shipment/offshore/submit endpoint.

[vehecap]

@Jone-Torgersen @bonyfusbouvet Is this still relevant for the API? Seems the issue has been closed in the frontend repo.

[Jone-Torgersen]

@Jone-Torgersen @bonyfusbouvet Is this still relevant for the API? Seems the issue has been closed in the frontend repo.

This has sort of been redone with the implementation of the multi-step form, so I don't think it is relevant anymore.