Update changelog entry for 6.0.0

Signed-off-by: Kentaro Hayashi <[email protected]>

Author: kenhys

CHANGELOG.md

@@ -2,6 +2,69 @@
 
 About the past changelog entries, see [old CHANGELOG](CHANGELOG-v4.md) instead.
 
+## Release v6.0.0 - 2025/08/29
+
+### News
+
+* Update Ruby to 3.4.4
+* Update fluentd to 1.19.0
+* Update bundled gems
+
+### Core component
+
+* ruby v3.4.4 (update)
+* jemalloc v3.6.0
+* OpenSSL 3.4.0 Windows
+* OpenSSL 3.0.8 macOS
+* gems
+  * fluentd v1.19.0 (update)
+  * msgpack 1.8.0 (update)
+  * oj 3.16.11 (update)
+  * webrick 1.9.1 (update)
+  * openssl 3.3.0
+
+### Bundled plugins and gems
+
+* aws-partitions v1.1110.0 (update)
+* aws-sdk-core v3.225.0 (update)
+* aws-sdk-kms v1.102.0 (update)
+* aws-sdk-s3 v1.189.0 (update)
+* aws-sdk-sqs v1.96.0 (update)
+* aws-sigv4 v1.12.0 (update)
+* elasticsearch v9.0.3 (update)
+* fluent-diagtool v1.0.5
+* fluent-plugin-elasticsearch v6.0.0 (update)
+* fluent-plugin-fluent-package-notifier v0.1.0 (new)
+* fluent-plugin-flowcounter-simple 0.1.0
+* fluent-plugin-kafka v0.19.4 (update)
+* fluent-plugin-metrics-cmetrics v0.1.2
+* fluent-plugin-obsolete-plugins v0.1.1 (new)
+* fluent-plugin-opensearch v1.1.5 (update)
+* fluent-plugin-prometheus v2.2.1 (update)
+* fluent-plugin-prometheus_pushgateway v0.2.1 (update)
+* fluent-plugin-record-modifier v2.2.0 (update)
+* fluent-plugin-rewrite-tag-filter v2.4.0
+* fluent-plugin-s3 v1.8.3 (update)
+* fluent-plugin-sd-dns 0.1.0
+* fluent-plugin-systemd v1.1.0 (update)
+* fluent-plugin-td v1.2.0
+* fluent-plugin-utmpx v0.5.0
+* fluent-plugin-webhdfs v1.6.0 (update)
+* mini_portile2 v2.8.9 (update)
+* prometheus-client v4.2.4 (update)
+* rdkafka v0.21.0 (update)
+* ruby-kafka v1.5.0
+* systemd-journal v2.0.0 (update)
+* td-client v2.0.0 (update)
+* webhdfs v0.11.0 (update)
+
+On Windows
+
+* fluent-plugin-parser-winevt_xml v0.2.8 (update)
+* fluent-plugin-windows-exporter v1.0.0
+* winevt_c v0.11.2 (update)
+* nokogiri v1.18.8 (update)
+
 ## Release v5.0.7 - 2025/05/16
 
 ### News