add auto/light/dark mode for docs #2583

Job	Run time
build-windows	1m 48s
build-linux-lint	11s
build-linux-test-component (buildx)	3m 22s
build-linux-test-component (test_compose.py)	7m 7s
Render docs	1m 23s
build-linux-test-component (test_config.py)	1m 7s
build-linux-test-component (test_container.py)	7m 59s
build-linux-test-other	1m 11s
build-linux-test-component (test_context.py)	58s
build-linux-test-component (test_image.py)	1m 27s
build-linux-test-component (test_manifest.py)	56s
build-linux-test-component (test_network.py)	1m 28s
build-linux-test-component (test_node.py)	1m 27s
build-linux-test-component (test_plugin.py)	48s
build-linux-test-component (test_pod.py)	1m 9s
build-linux-test-component (test_service.py)	2m 52s
build-linux-test-component (test_stack.py)	1m 35s
build-linux-test-component (test_swarm.py)	1m 12s
build-linux-test-component (test_system.py)	1m 30s
build-linux-test-component (test_task.py)	56s
build-linux-test-component (test_volume.py)	1m 2s
	41m 28s

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