Update tutorial to use new DDT data and download FITS files in the RTD build #853

Job	Run time
tests / Load tox environments	14s
allowed-fail-tests / Load tox environments	13s
allowed-fail-tests / py311-devdeps (ubuntu-latest)	4m 48s
tests / py312 (ubuntu-latest)	4m 45s
tests / py311 (ubuntu-latest)	3m 41s
tests / py310-online (windows-latest)	4m 38s
tests / py39 (macos-latest)	4m 46s
tests / build_docs-notebooks (ubuntu-latest)	4m 48s
tests / py39-oldestdeps (ubuntu-latest)	4m 34s
publish	1s
notify	1s
	32m 29s

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