Returns the list of all metadata fields (both custom and built-in) for the knowledge base, along with the count of documents using each field.
API Key authentication. For all API requests, include your API Key in the Authorization HTTP Header, prefixed with Bearer. Example: Authorization: Bearer {API_KEY}. Strongly recommend storing your API Key on the server-side, not shared or stored on the client-side, to avoid possible API-Key leakage that can lead to serious consequences.
Knowledge base ID.