docs: update changelog for integrations/mongodb_atlas (#2479)

* Update changelog for integrations/mongodb_atlas

* Update changelog for MongoDB DocumentStore features

---------

Co-authored-by: davidsbatista <7937824+davidsbatista@users.noreply.github.com>
Co-authored-by: David S. Batista <dsbatista@gmail.com>

Author: HaystackBot

integrations/mongodb_atlas/CHANGELOG.md

@@ -1,5 +1,21 @@
 # Changelog
 
+## [integrations/mongodb_atlas-v3.4.0] - 2025-10-29
+
+### 🚀 Features
+
+- Add `delete_all_documents()` operation to MongoDB DocumentStore (#2401)
+
+### 📚 Documentation
+
+- Add pydoc configurations for Docusaurus (#2411)
+
+### 🧹 Chores
+
+- Remove black (#1985)
+- Standardize readmes - part 2 (#2205)
+
+
 ## [integrations/mongodb_atlas-v3.3.0] - 2025-06-18
 
 ### 🐛 Bug Fixes