Add release notes for 1.27.3 (#5528)

Author: ikhoon

site/src/pages/release-notes/1.27.3.mdx

@@ -0,0 +1,20 @@
+---
+date: 2024-03-26
+---
+
+## 🛠️ Bug fixes
+
+- You no longer see `NullPointerException` when creating Thrift clients in a multi-threaded environment. #5497
+- `IllegalReferenceCountException` no longer occurs during WebSocket handshake. #5495
+- When a client sends a `CLOSE` frame, the user provided subscription is correctly closed. #5482
+
+## 🙇 Thank you
+
+<ThankYou usernames={[
+  'ikhoon',
+  'jrhee17',
+  'mauhiz',
+  'minwoox',
+  'tobias-',
+  'trustin'
+]} />