Decouple the grid config from the experiment definition (hash).

We often want to change the grid config for the same "experiment" but triage assigns it a new experiment hash. This is counter-intuitive. The grid gets encoded in the model group "model_type" and "hyperparameters" so there is no need to encode it in a experiment hash.

No files or tests are named. Start by tracing where the experiment hash is generated from the experiment definition and where grid configuration feeds model_type and hyperparameters. Done means changing the grid configuration no longer changes the experiment hash, while the model group still records the grid.

Written by the indexing model from the issue text.