Serialize the container_filesystem and image_filesystem in addition for file stats.

[kannon92]

What type of PR is this?

/kind feature

What this PR does / why we need it:

While testing the split filesystem test case, I found out that we weren't reporting which json object corresponded to which filesystem.

We were not serializing the key. This PR will serialize the image_filesystem and container_filesystem for yaml, json and go-template.

Before this PR, we were returning the following object for json output (default):

{
  "status": {
      {
        "timestamp": "1701985250615496190",
        "fsId": {
          "mountpoint": "/disk/containers/overlay-images"
        },
        "usedBytes": {
          "value": "20844"
        },
        "inodesUsed": {
          "value": "16"
        }
"status":      {
        "timestamp": "1701985250615496190",
        "fsId": {
          "mountpoint": "/disk/containers/overlay-images"
        },
        "usedBytes": {
          "value": "20844"
        },
        "inodesUsed": {
          "value": "16"
        }
      }
    ]
  }
}

Now we return:

{
  "status": {
    "imageFilesystems": [
      {
        "timestamp": "1701985250615496190",
        "fsId": {
          "mountpoint": "/disk/containers/overlay-images"
        },
        "usedBytes": {
          "value": "20844"
        },
        "inodesUsed": {
          "value": "16"
        }
      }
    ],
    "containerFilesystems": [
      {
        "timestamp": "1701985250615496190",
        "fsId": {
          "mountpoint": "/disk/containers/overlay-images"
        },
        "usedBytes": {
          "value": "20844"
        },
        "inodesUsed": {
          "value": "16"
        }
      }
    ]
  }
}

For table, we will output the values of each entry in the filesystem and give a label for each type of filesystem.

Which issue(s) this PR fixes:

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Add a key for image and container filesystems.

[haircommander]

/approve

LGTM

[kannon92]

/cc @SergeyKanzhelev @saschagrunert

The original PR was correct but it wasn't ideal for observability/UX.

[saschagrunert]

Thanks for the follow-up!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: haircommander, kannon92, saschagrunert

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