When Kubelet has CRI stats enabled, the container runtime handles
container tracking and cAdvisor is only queried for the root container
stats. Discovering and watching all containers at startup is unnecessary
overhead in that mode.

Add a DisableContainerDiscovery option to HousekeepingConfig that skips
plugin initialization, cgroup watchers, subcontainer scanning, and the
global housekeeping loop. The root container is still created at startup
to serve node-level resource and filesystem stats. Other containers are
created lazily via getContainer() on first query.

Signed-off-by: Damien Grisonnet <dgrisonn@redhat.com>