Update tutorial to use new DDT data and download FITS files in the RTD build #860

Job	Run time
allowed-fail-tests / Load tox environments	9s
tests / Load tox environments	16s
allowed-fail-tests / py311-devdeps (ubuntu-latest)	6m 8s
tests / py312 (ubuntu-latest)	6m 28s
tests / py311 (ubuntu-latest)	6m 23s
tests / py310-online (windows-latest)	7m 47s
tests / py39 (macos-latest)	6m 18s
tests / build_docs-notebooks (ubuntu-latest)	8m 33s
tests / py39-oldestdeps (ubuntu-latest)	5m 28s
publish	0s
notify	0s
	47m 30s

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