Add `inputs.self.submodules` flake attribute #14819

Job	Run time
tests on ubuntu	13m 10s
eval	54s
vm_tests	16m 8s
Check Docker secrets present for installer tests	1s
tests on macos	14m 9s
installer test on ubuntu	34s
installer test on macos	1m 24s
flake_regressions	14m 41s
docker_push_image	0s
	1h 1m 1s

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