Add changelog and regenerated docs

Signed-off-by: Prem Kumar <prmsrswt@gmail.com>

CHANGELOG.md

@@ -19,6 +19,7 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 - [#2728](https://github.com/thanos-io/thanos/pull/2728) Query: Fixed panics when using larger number of replica labels with short series label sets.
 - [#2787](https://github.com/thanos-io/thanos/pull/2787) Update Prometheus mod to pull in prometheus/prometheus#7414.
 - [#2807](https://github.com/thanos-io/thanos/pull/2807) Store: decreased memory allocations while querying block's index.
+- [#2800](https://github.com/thanos-io/thanos/pull/2800) Query: Fix handling of `--web.external-prefix` and `--web.route-prefix`
 
 ### Changed
 

docs/components/query.md

@@ -314,7 +314,8 @@ Flags:
                                  returned gRPC certificates. See
                                  https://tools.ietf.org/html/rfc4366#section-3.1
       --web.route-prefix=""      Prefix for API and UI endpoints. This allows
-                                 thanos UI to be served on a sub-path. This
+                                 thanos UI to be served on a sub-path. Defaults
+                                 to the value of --web.external-prefix. This
                                  option is analogous to --web.route-prefix of
                                  Promethus.
       --web.external-prefix=""   Static prefix for all HTML links and redirect