Modify the changelog title to focus on functionality

Modify the changelog title to focus on the feature being added, not how
it's implemented (deep merging).

ee/changelogs/unreleased/5078-ci-include-deep-merge.yml

 ---
-title: Allow customization of included CI configurations through deep merging
+title: Allow easier customization of included CI configurations
 merge_request: 5288
 author: King Chung Huang
 type: changed