deps: switch to runc/libcontainer/cgroups cgroup manager

[dtrudg]

Description of the Pull Request (PR):

Switch our cgroups management dependency from containerd/cgroups to opencontainers/runc/libcontainer/cgroups in order to ease implementation of systemd / unprivileged delegation etc.

This is the first step of the process of tidying up the cgroups manager code. At this point I have chosen to:

• Implement the existing cgroups.Manager interface with a new cgroups.ManagerLC in manager_libcontainer_linux.go. This avoids code changes in the runtime for this initial swap-out.
• Remove the old containerd/cgroups based cgroups.ManagerV1 and cgroups.ManagerV2.
• Retain the tests that were run against the old ManagerV1 and ManagerV2 and point them to ManagerLC.

The purpose of this approach is to first be happy that there's no impact from switching the dep out.

Refactoring will occur to address the facts that:

• The cgroups.Manager is a pretty nasty interface... and involves a bunch of messy code in the manager to implement.
• We can work much more directly with the libcontainer code's New/Set/Apply cycle.
• We need to extend for systemd and rootless cgroups management.
• Testing needs to be overhauled and expanded for the above.

Testing

The PR tests against cgroups v1 in CI (Ubuntu 20.04).

I have been testing locally against cgroups v2 unified on Fedora 35.

This fixes or addresses the following GitHub issues:

• Fixes Migrate from containerd/cgroups to opencontainers/runc/libcontainer/cgroups #530

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• Read the Guidelines for Contributing, and this PR conforms to the stated requirements.
• Added changes to the CHANGELOG if necessary according to the Contribution Guidelines
• Added tests to validate this PR, linted with make check and tested this PR locally with a make test, and make testall if possible (see CONTRIBUTING.md).
• Based this PR against the appropriate branch according to the Contribution Guidelines
• Added myself as a contributor to the Contributors File