Move `Dataset.meta["history"]` into `Dataset.history`

[tcompa]

This is to be re-assessed after a bit more real-life testing and improvement of the new history (ref #803).

Reasons for moving to a separate DB column:

1. We could better define its structure, on the line of

# Option 0
DatasetHistoryItemType = dict[Literal["worfklowtask", "status", "parallelization"]]
history: list[DatasetHistoryItemType]

# Option 1
class DatasetHistoryItem(Basemodel):
    worfklowtask: WorkflowTaskRead   # TBD
    status: WorkflowTaskStatusType
    parallelization: dict  # TBD

2. Better scope separation between Dataset.meta and Dataset.history:
   • We should avoid "leaking" the full history of a dataset to the task (which we are currently doing)
   • We could differentiate the current priority rules which are in-place for meta in some endpoints but in principle only apply to history