add `DOWNLOAD` staging action #1739

Job	Run time
test-getting_started / tests	2m 11s
test-tutorials (configuration.ipynb) / tests	1m 37s
test-tutorials (debugging.ipynb) / tests	2m 1s
test-tutorials (describing_tasks.ipynb) / tests	2m 42s
test-tutorials (multiple_pilots.ipynb) / tests	2m 40s
test-tutorials (profiling.ipynb) / tests	2m 0s
test-tutorials (raptor.ipynb) / tests	2m 1s
test-tutorials (staging_data.ipynb) / tests	2m 19s
test-tutorials (raptor_mpi.ipynb) / tests	5m 9s
test-tutorials (submission.ipynb) / tests	1m 50s
	24m 30s

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