onedrive: add support for no admin mode

Add tenant_url configuration option for accessing OneDrive/SharePoint
without admin privileges. When tenant_url is set, rclone uses the
SharePoint v2.0 API endpoint instead of the standard Microsoft Graph
API.

Co-Authored-By: KyokoMiki <161209740+kyokomiki@users.noreply.github.com>

docs/content/onedrive.md

@@ -237,6 +237,41 @@ credentials.
 anyone with the *Client ID* and *Client Secret* can access your
 OneDrive files. Take care to safeguard these credentials.
 
+### Non-admin access to Business OneDrive
+
+If you do not have admin access to your organization's OneDrive for
+Business, you can still connect by manually providing the SharePoint
+tenant URL and drive ID. This works by overriding the base API URL
+from the standard Microsoft Graph endpoint to the SharePoint v2.0
+endpoint.
+
+#### Steps to manually obtain credentials
+
+1. Open your browser and navigate to `https://[your-tenant].sharepoint.com/`
+2. Open Developer Tools (press F12) and go to the **Network** tab.
+3. Search for `driveAccessToken` in the network requests.
+4. Extract the following information from the response:
+   ```json
+   ".driveUrl": "{tenant_url}/v2.0/drives/{drive_id}",
+   ".driveAccessToken": "access_token={access_token}"
+   ```
+
+#### Rclone configuration
+
+Use the extracted values to configure your remote:
+
+```ini
+type = onedrive
+token = {"access_token":"{access_token}","token_type":"Bearer","refresh_token":"","expiry":"2045-12-31T23:59:59Z"}
+drive_id = {drive_id}
+tenant_url = {tenant_url}
+drive_type = business
+```
+
+Since the exact expiry time cannot be determined from web traffic,
+set the expiry to a future date. Note that the token will eventually
+expire and you will need to repeat the process to obtain a new one.
+
 ### Modification times and hashes
 
 OneDrive allows modification times to be set on objects accurate to 1