This change drops pod-centric metrics without a non-empty 'container' label.
Previously we dropped pod-centric metrics without a (pod, namespace) label set
however these can be critical for debugging.
The following provides a description and cardinality estimation based on the tests in a local cluster:
container_blkio_device_usage_total - useful for containers, but not for system services (nodes*disks*services*operations*2)
container_fs_.* - add filesystem read/write data (nodes*disks*services*4)
container_file_descriptors - file descriptors limits and global numbers are exposed via (nodes*services)
container_threads_max - max number of threads in cgroup. Usually for system services it is not limited (nodes*services)
container_threads - used threads in cgroup. Usually not important for system services (nodes*services)
container_sockets - used sockets in cgroup. Usually not important for system services (nodes*services)
container_start_time_seconds - container start. Possibly not needed for system services (nodes*services)
container_last_seen - Not needed as system services are always running (nodes*services)
container_spec_.* - Everything related to cgroup specification and thus static data (nodes*services*5)
