Move libcontainer/cgroups to a separate repository

[kolyshkin]

This is a continuation of #3007

The proposal (https://github.com/opencontainers/tob/blob/main/proposals/cgroups.md) is now accepted, this issue is to track implementation progress and to make sure we do it in time for v1.3.

Steps:

• libct/configs: move cgroup configs to libct/cgroups #4472
• libct/devices: move config to libct/cg/devices/config #4577
• Stop using libct/utils from libct/cgroups.
• Separate out libct/cgroups with complete git history, and move it to github.com/opencontainers/cgroups.