Fix example disk type values for LKE (ext-4 vs ext4)

[mabojars]

The Linode API supports either ext4 or raw for the disk type value, in LKE routes. The OpenAPI spec examples suggest ext-4 (with the -), which is incorrect. Requests using the ext-4 value yield a validation error response from the Linode API.

Example:

curl --request POST \
     --url https://api.linode.com/v4/lke/clusters \
     --header 'accept: application/json' \
     --header "authorization: Bearer YEEEEHAW!" \
     --header 'content-type: application/json' \
     --data '
{
  "k8s_version": "1.30",
  "label": "lkecluster12345",
  "node_pools": [
    {
      "autoscaler": {
        "enabled": true,
        "max": 12,
        "min": 3
      },
      "count": 6,
      "disks": [
        {
          "size": 1024,
          "type": "ext-4"
        }
      ],
      "labels": {
        "example.com/my-app": "teams"
      },
      "tags": [
        "example tag",
        "another example"
      ],
      "taints": [
        {
          "effect": "NoSchedule",
          "key": "example.com/my-app",
          "value": "teamA"
        },
        {
          "effect": "NoExecute",
          "key": "myapp.io/team",
          "value": "teamB"
        }
      ],
      "type": "g6-standard-4"
    }
  ],
  "region": "us-central",
  "tags": [
    "ecomm",
    "blogs"
  ]
}
'

{"errors": [{"reason": "Must be one of raw, ext4", "field": "node_pools[0].disks[0].type"}]}

It appears the ext-4 vs ext4 discrepancy was introduced in linode-api-docs/pull/283 (1 match for ext-4), and then disseminated in linode-api-docs/pull/956 (6 matches for ext-4).

This PR replaces all occurrences of ext-4 with the valid ext4, for LKE routes.

[mabojars]

@Vernholio will take over introducing these changes from here - thanks!