Prepare 6.6.0 release (OpenAPITools#15466)

* prepare 6.6.0 release

* update samples

Prepare 6.5.0 release (OpenAPITools#15099)

* 6.5.0 release

* update samples

Prepare 6.4.0 release (OpenAPITools#14748)

* prepare 6.4.0 release

* update samples

Prepare v6.3.0 release (OpenAPITools#14580)

* 6.3.0 release

* fix maven plugin test

* update samples

* update doc

* fix tests in windows

Prepare 6.2.1 release (OpenAPITools#13871)

* prepare 6.2.1 release

* revert change

* fix maven plugin test

* update meta

prepare 6.2.0 release (OpenAPITools#13514)

* set release version to 6.2.0

* update samples

* comment out rust server test in travis

6.1.0 release (OpenAPITools#13398)

Prepare 6.0.1 release (OpenAPITools#12762)

* update to v6.0.1

* update doc

* update samples

Prepare 6.0.0 release (OpenAPITools#12463)

* prepare 6.0.0 release

* update samples

* update meta codegen

Prepare 6.0.0 beta release (OpenAPITools#12039)

* update to 6.0.0-beta

* update samples