load-monitor: Move cgroups metrics to the load monitor

This merge request migrates all cgroups metrics from the GgroupManager to the newly merged LoadMonitor`.

Following the discussions here, it also drops all metrics for which there is an equivalent in cadvisor, to avoid duplication of metrics.

The following metrics were dropped in favour of cadvisor ones:

Gitaly	CAdvisor
gitaly_cgroup_memory_reclaim_attempts_total	container_memory_failures_total
gitaly_cgroup_cpu_usage_total	container_cpu_usage_seconds_total
gitaly_cgroup_cpu_cfs_periods_total	container_cpu_cfs_periods_total
gitaly_cgroup_cpu_cfs_throttled_periods_total	container_cpu_cfs_throttled_periods_total
gitaly_cgroup_cpu_cfs_throttled_seconds_total	container_cpu_cfs_throttled_seconds_total
gitaly_cgroup_procs_total	container_processes
gitaly_cgroup_memory_events_oom_total	container_oom_events_total
gitaly_cgroup_memory_pgfault_total	container_memory_failures_total{failure_type="pgfault"}
gitaly_cgroup_memory_pgmajfault_total	container_memory_failures_total{failure_type="pgmajfault"}

Closes https://gitlab.com/gitlab-org/gitaly/-/work_items/7140