Refactor system API (#13958)

### What problem does this PR solve?

- ping
- token
- log level

### Type of change

- [x] Refactoring


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Refactor**
* System endpoints consolidated under /api/v1/system: ping, health
check, and token management moved to the centralized API surface.
* Token management unified at /api/v1/system/tokens with
list/create/delete behavior.

* **Documentation**
  * API reference updated to reflect the new /api/v1/system paths.

* **Tests**
* Client fixtures and test utilities updated to use
/api/v1/system/tokens; one unit test for health/oceanbase status
removed.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

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

sdk/python/test/conftest.py

@@ -67,7 +67,7 @@ def get_api_key_fixture():
     except Exception as e:
         print(e)
     auth = login()
-    url = HOST_ADDRESS + "/v1/system/new_token"
+    url = HOST_ADDRESS + "/v1/system/tokens"
     auth = {"Authorization": auth}
     response = requests.post(url=url, headers=auth)
     res = response.json()