delete_dataset method and tests created (#1186)

### What problem does this PR solve?

This PR have completed both HTTP API and Python SDK for
'delete_dataset". In addition, there are tests for it.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

sdk/python/ragflow/ragflow.py

@@ -39,8 +39,23 @@ class RAGFlow:
         result_dict = json.loads(res.text)
         return result_dict
 
-    def delete_dataset(self, dataset_name=None, dataset_id=None):
-        return dataset_name
+    def delete_dataset(self, dataset_name):
+        dataset_id = self.find_dataset_id_by_name(dataset_name)
+        if not dataset_id:
+            return {"success": False, "message": "Dataset not found."}
+
+        res = requests.delete(f"{self.dataset_url}/{dataset_id}", headers=self.authorization_header)
+        if res.status_code == 200:
+            return {"success": True, "message": "Dataset deleted successfully!"}
+        else:
+            return {"success": False, "message": f"Other status code: {res.status_code}"}
+
+    def find_dataset_id_by_name(self, dataset_name):
+        res = requests.get(self.dataset_url, headers=self.authorization_header)
+        for dataset in res.json()['data']:
+            if dataset['name'] == dataset_name:
+                return dataset['id']
+        return None
 
     def list_dataset(self, offset=0, count=-1, orderby="create_time", desc=True):
         params = {