AIP-84 Migrate GET Dag Runs endpoint to FastAPI

[rawwar]

related to #42701

[rawwar]

@pierrejeambrun , as of now get dag runs does not raise 404 not found if dag id is invalid. Link.

Should we update it?

[pierrejeambrun]

@pierrejeambrun , as of now get dag runs does not raise 404 not found if dag id is invalid. Link.

Should we update it?

I think we should update it in the new FastAPI endpoint, I wouldn't bother fixing the legacy one though (it's not really a bug, more of an imprecision I would say, we can live with that in airflow 2.x). We can do the same as in get_tasks.

    """Get tasks for DAG."""
    dag: DAG = request.app.state.dag_bag.get_dag(dag_id)
    if not dag:
        raise HTTPException(status.HTTP_404_NOT_FOUND, f"Dag with id {dag_id} was not found")

[pierrejeambrun]

Added a really small tweak commit, ready to merge. (I didn't confirm my previous code review so the feedback never came through 🤦)

Thanks!