[DRAFT] add the creation of a timeline

From https://github.com/equinor/dot-archive/issues/720

> To be able to create an ID and DT, it would be good to implement a timeline possibility where it is possible to create a first initial timeline of the occurring decisions and uncertainties.

The timeline has similarities with the compact ID but may differ (where do we place the latent variables such as the state of the car in the timeline?).
Having a timeline before creating the ID may help setting arcs correctly. E.g. if arcs are added to the ID which do not respect the timeline, a warning or an error should be raised.

No files, tests, or entry points are identified. Start by clarifying the timeline data model, how latent variables such as the car state are placed, and how timeline ordering should constrain ID arcs; done requires an agreed design and validation behavior.

Written by the indexing model from the issue text.