release notes 9.0.4

Author: l-trotta

docs/release-notes/9-0-4.md

@@ -0,0 +1,31 @@
+---
+navigation_title: "9.0.4"
+---
+# Elasticsearch Java Client 9.0.4 [elasticsearch-java-client-904]
+
+Discover what changed in the 9.0.4 version of the java client. 
+
+### Features and enhancements [elasticsearch-java-client-900-features-enhancements]
+
+::::{dropdown} Added callbacks to Rest5Client builder
+Rest5ClientBuilder now has the same level of in depth configuration the Legacy RestClientBuilder has, allowing to customize the underlying Apache HttpClient through callback functions; for example, this is how to configure the IOReactor's thread count:
+```java
+Rest5ClientBuilder builder = Rest5Client
+    .builder(new HttpHost("localhost", 9200))
+    .setHttpClientConfigCallback(c -> c
+        .setIOReactorConfig(IOReactorConfig.custom()
+            .setIoThreadCount(1).build()
+        )
+    );
+```
+And this is how to customize the response timeout:
+```java
+Rest5ClientBuilder builder = Rest5Client
+    .builder(new HttpHost("localhost", 9200))
+    .setRequestConfigCallback(r -> r
+        .setConnectTimeout(Timeout.of(5000, TimeUnit.MILLISECONDS))
+        .setResponseTimeout(Timeout.of(30000, TimeUnit.MILLISECONDS))
+        .build()
+    );
+```
+::::

docs/release-notes/toc.yml

@@ -2,3 +2,4 @@ toc:
   - file: index.md
   - file: known-issues.md
   - file: 9-0-0.md
+  - file: 9-0-4.md