feat(theme): Branded theming via brand.yml #2966

Job	Run time
routine / routine	7m 14s
website / pkgdown	7m 52s
R-CMD-check / setup	7s
R-CMD-check / macOS-latest (4.4.2)	2m 33s
R-CMD-check / windows-latest (4.4.2)	3m 57s
R-CMD-check / ubuntu-latest (devel)	2m 19s
R-CMD-check / ubuntu-latest (4.4.2)	2m 9s
R-CMD-check / ubuntu-latest (4.3.3)	2m 11s
R-CMD-check / ubuntu-latest (4.2.3)	2m 20s
R-CMD-check / ubuntu-latest (4.1.3)	2m 18s
R-CMD-check / ubuntu-latest (4.0.5)	2m 27s
Deploy to shinyapps.io	0s
	35m 27s

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