Update CI and instructions for antsibull-fileutils; add explicit dependency on antsibull-fileutils #1265

Job	Run time
Build devel docsite	6m 34s
Build stable docsite	6m 2s
Build simple docsite (extra options: --use-current --sphinx-theme sphinx_rtd_theme)	4m 11s
Build simple docsite (extra options: --use-current --sphinx-theme sphinx_rtd_theme)	5m 5s
Build simple docsite (extra options: --no-indexes --squash-hierarchy --intersphinx ansible7:https://docs.ansible.com/ansible/6/ community.crypto --collection-version 2.0.0)	1m 14s
Build simple docsite (extra options: --no-indexes --squash-hierarchy --intersphinx ansible7:https://docs.ansible.com/ansible/6/ community.crypto --collection-version 2.0.0)	1m 24s
Build simple docsite (extra options: --use-current --use-html-blobs --no-breadcrumbs community.crypto community.docker --extra-conf antsibull_ext_color_scheme=none)	1m 39s
Build simple docsite (extra options: --use-current --output-format simplified-rst community.crypto community.docker)	2m 12s
	28m 21s

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