[Doc][Serve] Add missing imports to autoscaling policy example (#57896)

## Description
Add missing imports to autoscaling policy example

## Related issues
Link related issues:
#57876 (comment)

---------

Signed-off-by: daiping8 <dai.ping88@zte.com.cn>
Signed-off-by: Ping Dai <dai.ping88@zte.com.cn>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: daiping8

doc/source/serve/doc_code/autoscaling_policy.py

@@ -24,6 +24,10 @@ def scheduled_batch_processing_policy(
 
 
 # __begin_custom_metrics_autoscaling_policy__
+from typing import Any, Dict
+from ray.serve.config import AutoscalingContext
+
+
 def custom_metrics_autoscaling_policy(
     ctx: AutoscalingContext,
 ) -> tuple[int, Dict[str, Any]]:
@@ -46,10 +50,12 @@ def custom_metrics_autoscaling_policy(
 
 
 # __begin_application_level_autoscaling_policy__
-from ray.serve._private.common import DeploymentID
 from typing import Dict, Tuple
 from ray.serve.config import AutoscalingContext
 
+from ray.serve._private.common import DeploymentID
+from ray.serve.config import AutoscalingContext
+
 
 def coordinated_scaling_policy(
     contexts: Dict[DeploymentID, AutoscalingContext]