chore: rename what's new file and add a release date

Author: vnikolova

ktor.tree

@@ -381,7 +381,7 @@
 
     <toc-element toc-title="Releases">
         <toc-element topic="releases.md"/>
-        <toc-element topic="Whats-new-in-Ktor-3-2-0.md"/>
+        <toc-element topic="whats-new-320.md"/>
         <toc-element topic="migration-to-20x.md"
                      accepts-web-file-names="migrating-2.html"/>
         <toc-element topic="migration-to-22x.md"

topics/Whats-new-in-Ktor-3-2-0.md topics/whats-new-320.mdtopics/Whats-new-in-Ktor-3-2-0.md renamed to topics/whats-new-320.md

@@ -1,6 +1,8 @@
+[//]: # (title: What's new in Ktor 3.2.0)
+
 <show-structure for="chapter,procedure" depth="2"/>
 
-# What's new in Ktor 3.2.0
+_[Released: June 12, 2025](releases.md#release-details)_
 
 Here are the highlights for this feature release: