### 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>
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