feat(theme): Branded theming via brand.yml #2996

Job	Run time
R-CMD-check / setup	47s
routine / routine	5m 31s
website / pkgdown	4m 36s
R-CMD-check / macOS-latest (4.4.2)	2m 39s
R-CMD-check / windows-latest (4.4.2)	3m 51s
R-CMD-check / ubuntu-latest (devel)	3m 26s
R-CMD-check / ubuntu-latest (4.4.2)	3m 28s
R-CMD-check / ubuntu-latest (4.3.3)	2m 23s
R-CMD-check / ubuntu-latest (4.2.3)	3m 40s
R-CMD-check / ubuntu-latest (4.1.3)	3m 6s
R-CMD-check / ubuntu-latest (4.0.5)	2m 59s
Deploy to shinyapps.io	0s
	36m 26s

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