Missing some fields to support Stats API on Docker host uses cgroup2

[xruins]

Docker Engine 20.10.0+ supports cgroup2 and uses it by default.

Support cgroup2 moby/moby#40174 moby/moby#40657 moby/moby#40662
cgroup2: use “systemd” cgroup driver by default when available moby/moby#40846

(cf. https://docs.docker.com/engine/release-notes/#20100 )

The output of Docker Stats API varies depending on the version of cgroup used by Docker Engine.
Especially, Stats.MemoryStats.Stats for cgroup2 host much differ from the one of cgroup.

(definition for cgroup v1)
https://github.com/moby/moby/blob/548614694305d10e25665b4a7d0f61b025d47dd1/daemon/daemon_unix.go#L1439-L1470

(definition for cgroup v2)
https://github.com/moby/moby/blob/548614694305d10e25665b4a7d0f61b025d47dd1/daemon/daemon_unix.go#L1544-L1577

Currently, Stats (https://github.com/fsouza/go-dockerclient/blob/main/container_stats.go#L26) struct has only fields for cgroup v1, so it would be better to add the fields for cgroup v2 as well.
https://github.com/fsouza/go-dockerclient/blob/main/container_stats.go#L26