add `DOWNLOAD` staging action #1741

Job	Run time
test-getting_started / tests	2m 3s
test-tutorials (configuration.ipynb) / tests	1m 28s
test-tutorials (describing_tasks.ipynb) / tests	2m 57s
test-tutorials (debugging.ipynb) / tests	2m 26s
test-tutorials (multiple_pilots.ipynb) / tests	3m 6s
test-tutorials (profiling.ipynb) / tests	2m 32s
test-tutorials (raptor.ipynb) / tests	2m 7s
test-tutorials (staging_data.ipynb) / tests	2m 4s
test-tutorials (submission.ipynb) / tests	1m 33s
test-tutorials (raptor_mpi.ipynb) / tests	4m 17s
	24m 33s

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