Resolve data model discrepancies

[markusdregi]

Why?
These discrepancies frequently hinders development progress, as well as it introduces new and solidifies old shortcuts in the implementation. It would also be beneficial for future concept discussions if the data model was more established in the team and shared between ert2, ert3 and ert-storage.

Definition of Done
The current data model is documented, implemented in ert-storage, represented by the ERT Data API and is sufficient to serve as a data model for both ERT2 and ERT3. In particular, the utilised part of the data model by ERT2 should be a subset of what ERT3 utilises. Also, the user-data field should no longer be utilised by ERT2 nor ERT3. Last, webviz-ert should function on top of the updated API.

As a consequence, the "global records" __ensemble_records__ should disappear from the ert.storage module.

Related issues:

• Align ERT2 and ERT3 parameter model #2450
• Move userdata from Record to RecordInfo ert-storage#195
• Allow NumericalRecordTree as an ouput record in ensemble config #2698
• Unable to clean ensemble records - will put ert3 in an unrunnable state. #2731
• Propagate scope of data into ert-storage #1631

[sondreso]

Closing this issue as the project has taken a different direction than indicated in this milestone