Refactor module options and support rootless k3s & nix-snapshotter #521

Job	Run time
lint (golangci-lint)	1m 4s
build (nix-snapshotter)	22s
build (image-hello)	26s
build (image-redis)	23s
build (image-redisWithShell)	23s
integration-test (snapshotter)	3m 7s
integration-test (kubernetes)	3m 56s
integration-test (k3s)	12m 55s
integration-test (k3s-external)	13m 34s
integration-test (k3s-rootless)	13m 17s
	49m 27s

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