adding 2.16.1 release notes (#466)

* adding 2.16.1 release notes

* Update content/release-notes/2.16.1.md

Co-authored-by: Stefano Fiorucci <[email protected]>

---------

Co-authored-by: Stefano Fiorucci <[email protected]>

Author: davidsbatista

content/release-notes/2.16.1.md

@@ -0,0 +1,13 @@
+---
+title: Haystack 2.16.1
+description: Release notes for Haystack 2.16.1
+toc: True
+date: 2025-07-06
+last_updated: 2025-07-06
+tags: ["Release Notes"]
+link: https://github.com/deepset-ai/haystack/releases/tag/v2.16.1
+---
+
+## 🐛 Bug Fixes
+
+-   Improved validation in the `ChatMessage.from_user` class method. The method now raises an error if neither `text` nor `content_parts` are provided. It does not raise an error if `text` is an empty string.