Update tutorial to use new DDT data and download FITS files in the RTD build #855

Job	Run time
tests / Load tox environments	11s
allowed-fail-tests / Load tox environments	12s
tests / py312 (ubuntu-latest)	5m 14s
tests / py311 (ubuntu-latest)	3m 53s
tests / py310-online (windows-latest)	8m 17s
tests / py39 (macos-latest)	7m 48s
tests / build_docs-notebooks (ubuntu-latest)	6m 4s
tests / py39-oldestdeps (ubuntu-latest)	5m 27s
allowed-fail-tests / py311-devdeps (ubuntu-latest)	5m 26s
publish	0s
notify	0s
	42m 32s

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