Add additive categories infrastructure #3899

Job	Run time
nix	2m 17s
quick-build (supported, ubuntu-latest)	3m 36s
quick-build (latest, ubuntu-latest)	3m 27s
quick-build (dev, ubuntu-latest)	3m 32s
opam-build (latest, ubuntu-latest)	4m 40s
build (latest)	3m 17s
opam-build (supported, ubuntu-latest)	4m 15s
build (supported)	3m 49s
build (dev, --warnings)	3m 49s
opam-build (dev, ubuntu-latest)	4m 15s
doc-alectryon	16m 13s
doc-dep-graphs	8m 11s
coqchk (latest)	2m 13s
coqchk (dev)	1m 59s
coqchk (supported)	2m 24s
doc-coqdoc	1m 43s
install (supported)	1m 49s
doc-timing	1m 55s
install (latest)	1m 57s
install (dev)	1m 47s
deploy-doc	0s
delete-artifacts	7s
	1h 17m 15s

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