Add changelog for 0.20.0

CHANGELOG.md

+## 0.20.0 (2024-05-27)
+
+### Added (1 change)
+
+- [Auto URL-encode state name](components/opentofu@43148c5485b5b83cc858abb39f2033f579d2030c) ([merge request](components/opentofu!75))
+
 ## 0.19.0-rc1 (2024-05-15)
 
 ### Added (1 change)