[Chat][Doctrine] Update CHANGELOG for DoctrineDbalMessageStore rework

Author: Tiriel

src/chat/src/Bridge/Doctrine/CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+0.8
+---
+
+ * [BC BREAK] `DoctrineDbalMessageStore::save()` now upserts a single row instead of inserting a new row on every call; the table schema changed from `(id, messages, added_at)` to `(messages, updated_at)`
+
 0.1
 ---