Add changelog for #6474 (#6518)

Signed-off-by: Filip Petkovski <filip.petkovsky@gmail.com>

CHANGELOG.md

@@ -66,6 +66,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#6405](https://github.com/thanos-io/thanos/pull/6405) Index Cache: Change postings cache key to include the encoding format used so that older Thanos versions would not try to decode it during the deployment of a new version.
 - [#6432](https://github.com/thanos-io/thanos/pull/6432) Receive: Remove duplicated `gopkg.in/fsnotify.v1` dependency
 - [#6479](https://github.com/thanos-io/thanos/pull/6479) Store: *breaking :warning:* Rename `thanos_bucket_store_cached_series_fetch_duration_seconds` to `thanos_bucket_store_series_fetch_duration_seconds` and `thanos_bucket_store_cached_postings_fetch_duration_seconds` to `thanos_bucket_store_postings_fetch_duration_seconds`.
+- [#6474](https://github.com/thanos-io/thanos/pull/6474) Store/Compact: Reduce a large amount of `Exists` API calls against object storage when synchronizing meta files in favour of a recursive `Iter` call.
 
 ### Removed