Add changelog feature entry for generated API error fix
Updates change log for feature entry for generated API errors.
### SDK Features
+* SDK generated errors are fixed to use pointer receivers preventing confusion, and potential impossible type assertions. The SDK will only return API generated API error types as pointers. This fix ensures Go's type system will catch invalid error type assertions.
### SDK Enhancements
* Update SDK's `go-jmespath` dependency to latest tagged version `0.3.0` ([#3205](https://github.com/aws/aws-sdk-go/pull/3205))
