chore: update changelog for 1.20 release

CHANGELOG.md

@@ -3,18 +3,25 @@
 This format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## Unreleased
+## [v1.20.0](https:/flipt-io/flipt/releases/tag/v1.20.0) - 2023-04-11
 
 ### Added
 
 - Support for 'namespacing' / multi-environments. All types can now belong to a namespace allowing you to seperate your flags/segments/etc.
 
 ### Changed
 
+- `sdk/go`: add details regarding the HTTP transport (#1435)
 - All existing objects have been moved to the 'default' namespace to be fully backward compatible.
 - Import/Export have been updated to be 'namespace-aware'
 - Dependency updates
 
+### Fixed
+
+- `cmd/import`: re-open migration after dropping on import
+- protojson to use DiscardUnknown option for backwards compatibility (#1453)
+- `rpc/flipt`: move all openapi annotations into yaml file (#1437)
+
 ## [v1.19.3](https:/flipt-io/flipt/releases/tag/v1.19.3) - 2023-03-22
 
 ### Changed