Update changelogs from fern repo (#438)

Co-authored-by: tstanmay13 <[email protected]>

Author: fern-support

fern/products/sdks/overview/java/changelog/2025-08-13.mdx

@@ -0,0 +1,20 @@
+## 2.40.0
+**`(feat):`** Add support for client-side default parameter values via `use-default-request-parameter-values` flag. 
+When enabled, query and header parameters with defaults become Optional types and defaults are automatically 
+applied when not provided. Example:
+
+```yaml
+customConfig:
+  use-default-request-parameter-values: true
+```
+
+Generated code:
+```java
+// Parameters with defaults become Optional
+private final Optional<Integer> perPage;  // Has default: 50
+
+// Defaults are applied automatically
+QueryStringMapper.addQueryParameter(httpUrl, "per_page", request.getPerPage().orElse(50), false);
+```
+
+