Refactor module options and support rootless k3s & nix-snapshotter #522

Job	Run time
lint (golangci-lint)	1m 3s
build (nix-snapshotter)	27s
build (image-hello)	19s
build (image-redis)	22s
build (image-redisWithShell)	23s
integration-test (snapshotter)	1m 30s
integration-test (kubernetes)	2m 23s
integration-test (k3s)	1m 42s
integration-test (k3s-external)	1m 45s
integration-test (k3s-rootless)	1m 59s
	11m 53s

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