[REQ][Java][resttemplate] Add templated server support to Java resttemplate client

Created by: trussell314

Description

Would like to to see support for new ServerConfiguration/ServerVariable added to the Java resttemplate client templates, similar to what was added in #4998 for the base client and jersey2.

openapi-generator version

4.2.3

Related issues/PRs

#4998

Suggest a fix/enhancement

I am willing to make this enhancement (with a little guidance from the group). Would basically use the original change as an example.