Update tutorial to use new DDT data and download FITS files in the RTD build #854

Job	Run time
tests / Load tox environments	16s
allowed-fail-tests / Load tox environments	19s
tests / py312 (ubuntu-latest)	5m 5s
tests / py311 (ubuntu-latest)	3m 28s
tests / py310-online (windows-latest)	7m 32s
tests / py39 (macos-latest)	6m 33s
tests / build_docs-notebooks (ubuntu-latest)	10m 40s
tests / py39-oldestdeps (ubuntu-latest)	4m 53s
allowed-fail-tests / py311-devdeps (ubuntu-latest)	6m 41s
publish	0s
notify	0s
	45m 27s

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