Ensemble inheritance / parent

For feature restructuring of ensemble configuration, I suggest to introduce a concept of inheritance / parent. In this way we can connect e.g. ensembles that are restarts of other ensembles to their "parent ensemble" (or even multiple levels if restart if restart). In this way, the restarted ensembles can utilize data from the parent, without having to store and/or configure the data multiple times (or symlinks and so on). Could be initial inplace data, grid data, simulation history, maps, seismic +++

The issue names ensemble configuration and data such as initial inplace data, grid data, simulation history, maps, and seismic data, but no files, tests, or entry points. Start by locating the ensemble configuration model and its existing restart handling; done would require a defined parent relationship that supports reuse across the listed data without duplicate storage or configuration.

Written by the indexing model from the issue text.