added Ditto 3.5.9 release notes

Signed-off-by: Thomas Jäckle <thomas.jaeckle@beyonnex.io>

documentation/src/main/resources/_data/sidebars/ditto_sidebar.yml

@@ -23,6 +23,9 @@ entries:
       - title: Release Notes
         output: web
         folderitems:
+          - title: 3.5.9
+            url: /release_notes_359.html
+            output: web
           - title: 3.5.8
             url: /release_notes_358.html
             output: web

documentation/src/main/resources/pages/ditto/release_notes_359.md

@@ -0,0 +1,46 @@
+---
+title: Release notes 3.5.9
+tags: [release_notes]
+published: true
+keywords: release notes, announcements, changelog
+summary: "Version 3.5.9 of Eclipse Ditto, released on 14.06.2024"
+permalink: release_notes_359.html
+---
+
+This is a bugfix release, no new features since [3.5.8](release_notes_358.html) were added.
+
+## Changelog
+
+Compared to the latest release [3.5.8](release_notes_358.html), the following changes and bugfixes were added.
+
+### Bugfixes
+
+This is a complete list of the
+[merged pull requests](https://github.com/eclipse-ditto/ditto/pulls?q=is%3Apr+milestone%3A3.5.9).
+
+#### Fix performance regression issue when running against MongoDB 6 - part 3
+
+In Ditto [3.5.7](release_notes_357.html) and [3.5.8](release_notes_358.html) a MongoDB `aggregation` query done by Ditto 
+as part of background deletion was aimed to be optimized.  
+This fix provided in PRs [#1956](https://github.com/eclipse-ditto/ditto/pull/1956) and [#1961](https://github.com/eclipse-ditto/ditto/pull/1961) however were not completely sufficient to fix the performance
+and reduce the disk read IOPS.
+
+PR [#1964](https://github.com/eclipse-ditto/ditto/pull/1964) now in total adds 3 new indexes to the "snapshot" collections.  
+Those however are not configured by default, they must be configured as documented in the newly added 
+[MongoDB tuning](installation-operating.html#mongodb-tuning) section: 
+[Background aggregation queries](installation-operating.html#background-aggregation-queries).
+
+If you encounter performance issues and many disk read IOPS done in MongoDB version 6 (and maybe above), please check
+those settings.
+
+
+### Helm Chart
+
+The [Ditto Helm Chart](https://github.com/eclipse-ditto/ditto/tree/master/deployment/helm) contained some configuration 
+bugs and enhancements which are also addressed with this bugfix release.
+
+#### Make logstash buffer sizes configurable
+
+PR [#1963](https://github.com/eclipse-ditto/ditto/pull/1963) make the logstash buffer sizes used in `logback.xml` files
+of the Ditto services configurable via environment variables.  
+The configuration were also exposed to the Ditto Helm chart in that PR.