Upload a file to managed-files storage

{
  "path": "Audiodateien",
  "name": "music.mp3",
  "url": "https://example.com/file.mp3",
  "base64": "data:image/png;base64,iVBORw0KGgo..."
}

{
  "success": true,
  "file": {
    "name": "string",
    "path": "string",
    "url": "string",
    "size": 1,
    "contentType": "string"
  }
}