Java: Add release notes for release 5.9.0 (#1810)

* Add new release notes

* fix: code formatting

---------

Co-authored-by: Johannes Schneider <johannes.schneider03@sap.com>

docs-java/release-notes/release-notes-0-to-14.mdx

@@ -1,3 +1,31 @@
+## 5.9.0 - May 13, 2024
+
+[All Release Changes](https://github.com/SAP/cloud-sdk-java/releases/tag/rel%2F5.9.0)
+
+### 🔧 Compatibility Notes
+
+- Deprecate the `BtpServiceOptions.IasOptions.withTargetUri` method overloads.
+  As a replacement, users should use the corresponding `BtpServiceOptions.AuthenticationServiceOptions.withTargetUri` method.
+  Additionally, the existing behavior of the deprecated methods has been changed:
+  They are no longer returning an instance of `BtpServiceOptions.IasOptions.IasTargetUri` but instead return now an instance of `BtpServiceOptions.AuthenticationServiceOptions.TargetUri`.
+  The `BtpServiceOptions.IasOptions.IasTargetUri` class is also deprecated.
+
+  **Please Note**:
+  The deprecated methods will stay functioning (with the mentioned behavior changes) for a while to give users time to migrate to the new methods.
+  Nevertheless, we are planning to **remove** the deprecated methods and the class **still within version 5 of the SAP Cloud SDK**.
+
+### ✨ New Functionality
+
+- Support the [OAuth Refresh Token](https://help.sap.com/docs/connectivity/sap-btp-connectivity-cf/oauth-refresh-token-authentication) authentication type of the Destination Service.
+  Find more details on how to use the functionality in the [documentation](https://sap.github.io/cloud-sdk/docs/java/features/connectivity/btp-destination-service#about-the-destinationservice).
+- Service Bindings for the SAP XSUAA service (Service Identifier `xsuaa`) can now be converted into destinations just as any other supported service.
+  This is most useful when combined with the newly introduced `BtpServiceOptions.AuthenticationServiceOptions.withTargetUri` methods, which allows for communication between services that are backed by the same XSUAA instance.
+
+### 🐛 Fixed Issues
+
+- Fix a regression that was introduced with the SAP Cloud SDK 5.0 release where the principal would no longer be derived from a `Basic` authorization header, in cases where neither a JWT nor an OIDC token was present.
+- Fix a regression that was introduced with the SAP Cloud SDK 5.0 release where auth tokens sent by the Destination service would no longer be stored in the `cloudsdk.authTokens` destination property for non-HTTP destinations.
+
 ## 5.8.0 - April 22, 2024
 
 [All Release Changes](https://github.com/SAP/cloud-sdk-java/releases/tag/rel%2F5.8.0)