WIP: Customise the sunpy-sphinx-theme #885

Job	Run time
sdist_verify	14s
docs / Load tox environments	6s
allowed-fail-tests / Load tox environments	8s
tests / Load tox environments	6s
docs / build_docs-notebooks (ubuntu-latest)	1m 58s
tests / py312 (ubuntu-latest)	2m 4s
tests / py311 (ubuntu-latest)	1m 59s
tests / py311-online (windows-latest)	1m 52s
tests / py310 (macos-latest)	1m 52s
tests / py310-oldestdeps (ubuntu-latest)	1m 58s
allowed-fail-tests / py311-devdeps (ubuntu-latest)	1m 57s
publish	1s
notify	1s
	14m 16s

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