Display network information of checkpoints created with Podman

[rst0git]

checkpointctl currently shows IP address information for checkpoints created with CRI-O but not with Podman. For checkpoints created with Podman, this information is stored in network.status, which has content in a JSON format like the following example:

{
  "podman": {
    "interfaces": {
      "eth0": {
        "subnets": [
          {
            "ipnet": "10.88.0.9/16",
            "gateway": "10.88.0.1"
          }
        ],
        "mac_address": "f2:99:8d:fb:5a:57"
      }
    }
  }
}

To enable this feature, we need to extract the network.status file from the checkpoint and parse its content.