Allow degraded mode for Gitaly's Cgroups

https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/13092 outlines a current issue with the way Gitaly uses cgroups. Currently, startup will fail unless it can successfully setup the cgroup manager.

This is a problem on restarts. Because cgroups are ephemeral, and gitlab-ctl reconfigure is what sets up the cgroup root, when a gitaly node restarts the cgroup root might have disappeared, which prevents Gitaly from starting up.

We should not block Gitaly startup on Cgroups.

The simplest thing we can do is to fail open when Cgroups fail to set up. This would fall back on not using Cgroups for Git commands.

A second improvement we can make is to make Cgroup setup lazy. If it fails on startup, then kick off a background process to attempt to setup cgroups every few minutes.