Update docs for new Serverless GCP regions (elastic#1747)

This updates the
[Regions](https://www.elastic.co/docs/deploy-manage/deploy/elastic-cloud/regions)
and [Serverless
changelog](http://localhost:3000/release-notes/elastic-cloud-serverless/)
pages for the new GCP Mumbai and Belgium regions.

@xinglu-wang If you're the right person to ask, I'd appreciate if you
can let me know (here or in Slack) exactly when we should publish this
update.

Closes: elastic/platform-docs-team#685

---

<img width="616" alt="screen-regions"
src="https://github.com/user-attachments/assets/74a9f63b-7f12-4e00-938e-3e4ab7864a8a"
/>

---

<img width="629" alt="screen-changelog"
src="https://github.com/user-attachments/assets/d4b901fd-52df-47cb-bc93-fe18bba26691"
/>

Author: kilfoyle

deploy-manage/deploy/elastic-cloud/regions.md

@@ -49,4 +49,6 @@ The following GCP regions are currently available:
 
 | Region | Name |
 | :--- | :--- |
+| asia-south1 | Mumbai |
+| europe-west1 | Belgium |
 | us-central1 | Iowa |

release-notes/elastic-cloud-serverless/index.md

@@ -11,6 +11,12 @@ Review the changes, fixes, and more to {{serverless-full}}.
 
 For {{serverless-full}} API changes, refer to [APIs Changelog](https://www.elastic.co/docs/api/changes).
 
+## June 17, 2025 [serverless-changelog-06172025]
+
+### Features and enhancements [serverless-changelog-06172025-features-enhancements]
+
+* {{serverless-full}} is now available in two new Google Cloud Platform [regions](/deploy-manage/deploy/elastic-cloud/regions.md): GCP Belgium (`europe-west1`) and GCP Mumbai (`asia-south1`). 
+
 ## June 9, 2025 [serverless-changelog-06092025]
 
 ### Features and enhancements [serverless-changelog-06092025-features-enhancements]