chore(changelog): add v2.1.0 changelog

Author: slack

mkdocs.yml

@@ -84,6 +84,7 @@ pages:
     - Controller API v2.2: reference-guide/controller-api/v2.2.md
   - Changelogs:
     - v2.0.0: changelogs/v2.0.0.md
+    - v2.1.0: changelogs/v2.1.0.md
 theme_dir: themes/deis
 docs_dir: src
 markdown_extensions: