Add changelog entry for fixing the mattermost log file being owned by root

CHANGELOG.md

@@ -8,6 +8,10 @@ omnibus-gitlab repository.
 - Upgrade krb5 lib to 1.14.2
 - Create logrotate folders and configs even when the service is disabled
+8.10.3
+
+- Fix issue where mattermost log file is created by the root user
+
 8.10.2
 - Exclude standard ports from Host header