curl --request POST \
  --url https://api.callin.io/api/public/v1/knowledge-base/documents/file \
  --header 'Content-Type: multipart/form-data' \
  --header 'x-api-key: <api-key>' \
  --form 'groupName=<string>' \
  --form 'files=<string>' \
  --form files.items='@example-file'

{
  "success": true,
  "data": {
    "groupId": "<string>",
    "name": "<string>",
    "documents": [
      {
        "documentId": "<string>",
        "name": "<string>",
        "details": {
          "fileUrl": "<string>",
          "fileType": "<string>",
          "fileSize": 123
        },
        "metadata": {
          "createdAt": "2023-11-07T05:31:56Z",
          "createdBy": {
            "userId": "<string>",
            "userEmail": "<string>"
          }
        }
      }
    ],
    "metadata": {
      "allowedMb": 123,
      "usedMb": 123,
      "usedMbAfter": 123,
      "remainingMbAfter": 123
    }
  }
}