For #73503.

This PR:

• Changed pod log directory from /var/log/pods/UID to /var/log/pods/NAMESPACE_NAME_UID.

  • I tried the solution proposed in CRI: Include pod name and namespace in the CRI pod log directory #73503 (comment). It is too complex to implement and maintain. Since we never officially support in-place upgrade, let's only do best effort support.
  • We made several changes for backward compatibility:
    • Change 1: Whenever the container log path is needed, ContainerStatus.GetLogPath() is used to get the actual log path from the container runtime. This works for both containers with old log path and new log path.
    • Change 2: Pod log directory garbage collection handles both old log path and new log path.
  • With these changes, only minor problems left:
    • When getting container log stats, only new container log path is being used, because we want to avoid extra ContainerStatus calls. So if people do in-place upgrade, the log stats for existing containers will become empty.
    • For a newly created container in an existing pod sandbox, if the container runtime uses pod log directory passed in RunPodSandbox instead of CreateContainerRequest, the container log will be in the old pod log directory. In this case:
      • The symlink from /var/log/containers to /var/log/pods/NAMESPACE_NAME_UID won't work, because the container log is actually in /var/log/pods/UID.
      • The container log stats will be empty.
      • To handle this case properly, it is recommended for the container runtime to use the newest SandboxConfig in the CreateContainerRequest instead of caching and using the one passed in RunPodSandbox. Dockershim is handling this correctly, and we'll change containerd to do this as well. /cc @mrunalp

• Include container log inode usage as part of pod ephemeral storage for CRI stats provider. We were not doing that because cadvisor doesn't return accurate container log inode usage, but we do have that for CRI container runtimes. /cc @dashpole @jingxu97

• Include fsstats of log files under the pod log directory. Because we don't have log files under the pod log directory today, so this won't affect any existing functionality. Some sandbox runtimes, e.g. kata and gvisor, may have some pod level logs. This change makes it possible them to fsstats of those logs as part of pod ephemeral storage.

/cc @kubernetes/sig-node-pr-reviews

Change CRI pod log directory from `/var/log/pods/UID` to `/var/log/pods/NAMESPACE_NAME_UID`.

It is recommended to drain the node before upgrade, or reboot the node after upgrade.