Change to linking flow

[GFibrizo]

Problem

The model buyer has to be able to publish the requirements of the data needed for the training of a model, and the data owner should have a window of time that is wide enough to see the requirement, upload a dataset that fulfils those requirements and accept the request.

Solution

• Refactor the "link_dataset_to_model_id" endpoint. Split it into several.
  • 1 for receiving the requirements over the data
  • 1 to get all the requirements that have been sent so far (or the ones pending)
  • 1 to get the detail of a specific requirement of data
  • 1 to upload the dataset
  • 1 to accept the training (maybe this isn't a must)