Add GitLab 15.3 changelog

@Normo Could you please check the Changelog entry for GitLab 15.3. Thanks :)

docs/software/gitlab/changelog.md

@@ -2,6 +2,17 @@
 title: Changelog
 ---
 
+## 2022-09-08 - GitLab 15.3
+
+* Update GitLab to version 15.3
+    * [Create tasks in issues][15-3-tasks]
+    * [Submit merge request review with summary comment][15-3-summary]
+    * All details are available in the [Release Post][15-3-release-post]
+
+[15-3-tasks]: https://about.gitlab.com/releases/2022/08/22/gitlab-15-3-released/#create-tasks-in-issues
+[15-3-summary]: https://about.gitlab.com/releases/2022/08/22/gitlab-15-3-released/#submit-merge-request-review-with-summary-comment
+[15-3-release-post]: https://about.gitlab.com/releases/2022/08/22/gitlab-15-3-released/
+
 ## 2022-08-02 - GitLab 15.2
 
 * Update GitLab to version 15.2