Fix: Correct the API path (#15204)

Follow on PR #15146 to reslove the backwad compatability issue.

1. /agents/<attachment_id>/download ->
/agents/attachments/<attachment_id>/download

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

docs/references/http_api_reference.md

@@ -6908,18 +6908,18 @@ Failure:
 ##### Request example
 
 ```bash
-curl --request GET \
+curl --request GET \
      --url 'http://{address}/api/v1/agents/attachments/{attachment_id}/download?ext=pdf' \
      --header 'Authorization: Bearer <YOUR_API_KEY>' \
-     --output ./downloaded_attachment.pdf
+     --output ./downloaded_attachment.pdf
 ```
 
-##### Request parameters
+##### Request parameters
 
 - `attachment_id`: (*Path parameter*), `string`, *Required*
   The attachment ID whose file should be downloaded.
 - `ext`: (*Query parameter*), `string`, *Optional*
-  A file extension hint specifying the response's Content-Type. Defaults to `"markdown"`. Available values:
+  A file extension hint specifying the response's Content-Type. Defaults to `"markdown"`. Available values:
   - `"markdown"`
   - `"html"`
   - `"pdf"`
@@ -6929,15 +6929,15 @@ Downloads a runtime attachment previously uploaded via the [Upload document](#up
 
 #### Response
 
-Success:
+Success:
 
 Returns the file content as a binary stream with the relevant Content-Type header.
 
 Failure:
 
 ```json
-{
-    "code": 500,
+{
+    "code": 500,
     "message": "Internal server error"
 }
 ```