verbose log for cgroups_mkdir

[josedonizetti]

we are logging an error for cgroup_mkdir logs which are not related to a container, this is polluting tracee's output, let's change the log level to debug.

{"level":"error","ts":1691287215.0058243,"msg":"error processing control plane signal","error":"controlplane.(*Controller).processCgroupMkdir: failed to get lookup key 824648583784 from map containers_map: no such file or directory"}