Remove HttpClient Interfaces and Classes

[ryanjbaxter]

The classes and interfaces in org.springframework.cloud.commons.httpclient are only used by Spring Cloud OpenFeign. Other projects no longer use them. We can remove these classes and interfaces and move the necessary code to Spring Cloud OpenFeign. In addition Spring Framework 6 has removed support for Apache HttpClient v4 so we should be using HttpClient v5, which OpenFeign already has support for.