[MINOR] Add navigation for REST API document

### What changes were proposed in this pull request?

Add navigation for `REST API` document.

### Why are the changes needed?

`REST API` document does not have any navigation, which is better to add navigation to guide REST API.

<img width="1438" alt="image" src="https://github.com/user-attachments/assets/b5b3a14a-38d4-4769-bffb-3acd571d5dbb">

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

No.

Closes #2775 from SteNicholas/navigate-rest-api.

Authored-by: SteNicholas <programgeek@163.com>
Signed-off-by: mingji <fengmingxiao.fmx@alibaba-inc.com>

docs/decommissioning.md

@@ -69,7 +69,7 @@ Administrators perform decommissioning operation in two approaches:
   curl -X POST -H "Content-Type: application/json" -d '{"eventType":"DecommissionThenIdle","workers":[{"host":"192.168.15.140","rpcPort":"37359","pushPort":"38303","fetchPort":"37569","replicatePort":"37093"},{"host":"192.168.15.141","rpcPort":"37359","pushPort":"38303","fetchPort":"37569","replicatePort":"37093"}]}' http://ip:port/api/v1/workers/events
   ```
 
-Details of decommissioning interface can refer to [REST API](../webapi/#rest-api)
+Details of decommissioning interface can refer to [REST API](../restapi/#rest-api)
 
 ## Decommission Monitoring
 

docs/migration.md

@@ -22,11 +22,11 @@ license: |
 # Migration Guide
 
 # Upgrading from 0.5 to 0.6
-- 
+
 - Since 0.6.0, Celeborn has introduced a new RESTful API namespace: /api/v1, which uses the application/json media type for requests and responses.
    The `celeborn-openapi-client` SDK is also available to help users interact with the new RESTful APIs.
    The legacy RESTful APIs have been deprecated and will be removed in future releases.
-   Access the full [RESTful API documentation](./webapi.md) for detailed information.
+   Access the full [RESTful API documentation](./restapi.md) for detailed information.
   
   - The mappings of the old RESTful APIs to the new RESTful APIs for Master.
 

docs/monitoring.md

@@ -412,6 +412,6 @@ scrape_configs:
 
 ## REST API
 
-In addition to viewing the metrics, Celeborn also supports [REST API](webapi.md).
+In addition to viewing the metrics, Celeborn also supports [REST API](restapi.md).
 This gives developers an easy way to create new visualizations and monitoring tools for Celeborn and
 also easy for users to get the running status of the service.

mkdocs.yml

@@ -67,7 +67,9 @@ nav:
   - Deployment:
       - Overview: deploy.md
       - Kubernetes: deploy_on_k8s.md
-      - Monitoring: monitoring.md
+      - Monitoring:
+        - Overview: monitoring.md
+        - Rest API: restapi.md
       - Security: security.md
       - Quota Management: quota_management.md
       - Upgrading: upgrading.md