Prepare changelog for 9.0.0

Author: davidweterings

CHANGES

@@ -1,3 +1,14 @@
+9.0.0 (2020-08-14)
+------------------
+Note this release has some breaking changes regarding imports and a lot of code is now autogenerated.
+
+- Services are now generated by the RAML specification
+- Optimize import times for faster startup by only loading necessary schemas
+- Breaking: rename `commercetools.schemas.*` -> `commercetools._schema.*` since they are considered an implementation detail
+- Fix incorrect schema in various nested fields
+- Code generation now works with Python 3.8
+
+
 8.3.0 (2020-07-21)
 ------------------
 - Testing backend request mock parameters were case insensitive, causing expanding to fail in some cases