Test datasource credentials

Browse datasource folders Browse the remote folder hierarchy of a datasource without persisting anything. Connects to the external provider using the credentials in the payload and returns the immediate subfolders of ``parent_id`` (or the top-level entries when ``parent_id`` is ``null``). Use this to power a visual folder picker before submitting a datasource configuration via `PATCH /api/v1/workspaces/{id}` with a `datasource` payload. **Access:** any authenticated user. Supported providers and credentials: - **googledrive**: `service_account_file` (JSON string of the service account key file). When ``parent_id`` is omitted, returns the folders explicitly shared with the service account. - **sharepoint**: `client_id`, `client_secret`, `tenant_id`, `instance_url`, `site_name`. When both ``drive_id`` and ``parent_id`` are ``null``, returns the site's document libraries as ``kind="library"`` entries (each entry's ``id`` is the drive id). Pass that ``id`` back as ``drive_id`` (with ``parent_id=null``) to list the library root; pass it as ``drive_id`` together with a folder's ``id`` as ``parent_id`` to descend into a folder.