API: create dataset (#1106)

### What problem does this PR solve?

This PR have finished 'create dataset' of both HTTP API and Python SDK.
HTTP API:
```
curl --request POST --url http://<HOST_ADDRESS>/api/v1/dataset   --header 'Content-Type: application/json' --header 'Authorization: <ACCESS_KEY>' --data-binary '{
  "name": "<DATASET_NAME>"
}'
```

Python SDK:
```
from ragflow.ragflow import RAGFLow
ragflow = RAGFLow('<ACCESS_KEY>', 'http://127.0.0.1:9380')
ragflow.create_dataset("dataset1")

```

TODO: 
- ACCESS_KEY is the login_token when user login RAGFlow, currently.
RAGFlow should have the function that user can add/delete access_key.

### Type of change

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

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

sdk/python/test/test_dataset.py

@@ -0,0 +1,26 @@
+from test_sdkbase import TestSdk
+import ragflow
+from ragflow.ragflow import RAGFLow
+import pytest
+from unittest.mock import MagicMock
+from common import API_KEY, HOST_ADDRESS
+
+class TestDataset(TestSdk):
+
+    def test_create_dataset(self):
+        '''
+        1. create a kb
+        2. list the kb
+        3. get the detail info according to the kb id
+        4. update the kb
+        5. delete the kb
+        '''
+        ragflow = RAGFLow(API_KEY, HOST_ADDRESS)
+
+        # create a kb
+        res = ragflow.create_dataset("kb1")
+        assert res['code'] == 0 and res['message'] == 'success'
+        dataset_id = res['data']['dataset_id']
+        print(dataset_id)
+
+        # TODO: list the kb