Add changelog entries

Fixes thanos-io#2984

Signed-off-by: Goutham Veeramachaneni <gouthamve@gmail.com>

CHANGELOG.md

@@ -30,13 +30,15 @@ We use _breaking :warning:_ to mark changes that are not backward compatible (re
 - [#3245](https://github.com/thanos-io/thanos/pull/3245) Query Frontend: Add `query-frontend.org-id-header` flag to specify HTTP header(s) to populate slow query log (e.g. X-Grafana-User).
 - [#3431](https://github.com/thanos-io/thanos/pull/3431) Store: Added experimental support to lazy load index-headers at query time. When enabled via `--store.enable-index-header-lazy-reader` flag, the store-gateway will load into memory an index-header only once it's required at query time. Index-header will be automatically released after `--store.index-header-lazy-reader-idle-timeout` of inactivity.
  - This, generally, reduces baseline memory usage of store when inactive, as well as a total number of mapped files (which is limited to 64k in some systems.
+- [#3437](https://github.com/thanos-io/thanos/pull/3437) StoreAPI: Added `hints` field to `LabelNamesResponse` and `LabelValuesResponse`. Hints in an opaque data structure that can be used to carry additional information from the store and its content is implementation specific.
 
 ### Fixed
 
 - [#3257](https://github.com/thanos-io/thanos/pull/3257) Ruler: Prevent Ruler from crashing when using default DNS to lookup hosts that results in "No such hosts" errors.
 - [#3331](https://github.com/thanos-io/thanos/pull/3331) Disable Azure blob exception logging
 - [#3341](https://github.com/thanos-io/thanos/pull/3341) Disable Azure blob syslog exception logging
 - [#3414](https://github.com/thanos-io/thanos/pull/3414) Set CORS for Query Frontend
+- [#3437](https://github.com/thanos-io/thanos/pull/3437) Add external labels to Labels APIs.
 
 ### Changed