Track which Trial object is user-suggested

[ghost]

Describe the solution you'd like

It would be good if the Trial object had a user_suggested field which would allow us to track which trials are coming from user suggested parameter values.

This would help the user themselves in the case of non-in-order executions.
This would also allow the optimiser to have the ability not to drop them from distribution estimation even if linear_forgetting would otherwise make them remain unused.