Add time utils (#10849)

### What problem does this PR solve?

- Add time utilities and unit tests

### Type of change

- [x] Refactoring

---------

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

api/apps/user_app.py

@@ -34,13 +34,8 @@ from api.db.services.file_service import FileService
 from api.db.services.llm_service import get_init_tenant_llm
 from api.db.services.tenant_llm_service import TenantLLMService
 from api.db.services.user_service import TenantService, UserService, UserTenantService
-from api.utils import (
-    current_timestamp,
-    datetime_format,
-    download_img,
-    get_format_time,
-    get_uuid,
-)
+from common.time_utils import current_timestamp, datetime_format, get_format_time
+from api.utils import download_img, get_uuid
 from api.utils.api_utils import (
     construct_response,
     get_data_error_result,