Make an actual changelog title entry

- The changelog title was not human readable - instead was the branch
  name or the filename - doh!

changelogs/unreleased/remove-reactive-caching-redis-keys-after-use.yml → changelogs/unreleased/reactive-caching-self-cleanup.yml

 ---
-title: remove-reactive-caching-redis-keys-after-use
+title: Remove reactive caching value keys once the alive key has expired
 merge_request: 20111
 author:
 type: performance