[JAVA] Enable code generation for OpenFeign with Spring-Boot 2

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Description

When using generation library spring-cloud, code will be generated with import:

import org.springframework.cloud.netflix.feign.FeignClient;

But when one wants to use open feign with spring boot 2, we need the following:

import org.springframework.cloud.openfeign.FeignClient;

Solution: Setup property to switch between both import statements (JavaSpring library "spring-cloud)" -> "apiClient.mustache".

Swagger-codegen version

2.4.1

Swagger declaration file content or url

Command line used for generation

Steps to reproduce

Related issues/PRs

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