Allow declaration of project addons #10643

Job	Run time
Ruby 3.1 on ubuntu-latest	12m 0s
Ruby 3.2 on ubuntu-latest	13m 7s
lint_ruby	20s
Ruby 3.3 on ubuntu-latest	10m 18s
Ruby 3.1 on macos-latest	8m 52s
Ruby 3.2 on macos-latest	7m 51s
Ruby 3.3 on macos-latest	6m 41s
Ruby 3.1 on windows-latest	23m 17s
Ruby 3.2 on windows-latest	30m 3s
Ruby 3.3 on windows-latest	30m 3s
build_node (ubuntu-latest)	1m 6s
build_node (macos-latest)	1m 20s
build_node (windows-latest)	5m 25s
lint_node	27s
Verify Jekyll website builds	7s
	2h 30m 57s

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