add `DOWNLOAD` staging action #1727

Job	Run time
test-getting_started / tests	1m 58s
test-tutorials (configuration.ipynb) / tests	1m 23s
test-tutorials (debugging.ipynb) / tests	2m 1s
test-tutorials (describing_tasks.ipynb) / tests	2m 37s
test-tutorials (multiple_pilots.ipynb) / tests	2m 52s
test-tutorials (profiling.ipynb) / tests	2m 9s
test-tutorials (raptor.ipynb) / tests	1m 57s
test-tutorials (raptor_mpi.ipynb) / tests	5m 14s
test-tutorials (staging_data.ipynb) / tests	2m 4s
test-tutorials (submission.ipynb) / tests	1m 23s
	23m 38s

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