Prepare 4.3.1 release (OpenAPITools#6187)

* prepare 4.3.1 release

* update doc

4.3.0 release (OpenAPITools#5721)

Prepare 4.2.3 release (OpenAPITools#5172)

* release 4.2.3

* update readme

release 4.2.2 (OpenAPITools#4661)

Prepare 4.2.1 release (OpenAPITools#4494)

* prepare 4.2.1 release

* use stable version in test/example

Prepare 4.2.0 release (OpenAPITools#4333)

* remove snapshot

* update doc

prepare 4.1.3 release (OpenAPITools#4052)

Prepare v4.1.2 release (OpenAPITools#3873)

* update samples

* update date

Prepare 4.1.1 release (OpenAPITools#3756)

* 4.1.1 release

* update doc

Prepare 4.1.0 release (OpenAPITools#3597)

* update pom

* update doc

* update version

* add dep for nullable annotaiton