nit: remove taskgroup's tooltip from OL's AirflowJobFacet
Removing TaskGroup's tooltip from AirflowJobFacet that's included in DAG start event. The tooltip is already included in task level OpenLineage events and it might be long, so there is no need to duplicate that information. The DAG start event should only contain information necessary to deduce task dependencies and DAG structure, so the tooltip is not needed at that time.
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Rebased.