add changelog

Signed-off-by: yeya24 <yb532204897@gmail.com>

CHANGELOG.md

@@ -18,6 +18,7 @@ We use _breaking :warning:_ to mark changes that are not backward compatible (re
 - [#3700](https://github.com/thanos-io/thanos/pull/3700) ui: make old bucket viewer UI work with vanilla Prometheus blocks
 - [#2641](https://github.com/thanos-io/thanos/issues/2641) Query Frontend: Added `--query-range.request-downsampled` flag enabling additional queries for downsampled data in case of empty or incomplete response to range request.
 - [#3792](https://github.com/thanos-io/thanos/pull/3792) Receiver: Added `--tsdb.allow-overlapping-blocks` flag to allow overlapping tsdb blocks and enable vertical compaction
+- [#3686](https://github.com/thanos-io/thanos/pull/3686) Query: Added federated metric metadata support.
 
 ### Fixed