[Spring] Support @Validated

Description

Add support for @org.springframework.validation.annotation.Validated

IF useBeanValidation and performBeanValidation are true
THEN should be @Validated on generated Api & ApiController classes

Swagger-codegen version

3.0.18

Example pom.xml

<plugins>
  <plugin>
    <groupId>io.swagger.codegen.v3</groupId>
    <artifactId>swagger-codegen-maven-plugin</artifactId>
    <executions>
      <execution>
        ...
        <configuration>
          ...
          <language>spring</language>
          <configOptions>
            <useBeanValidation>true</useBeanValidation>
            <performBeanValidation>true</performBeanValidation>
          </configOptions>
        </configuration>
      </execution>
    </executions>
  </plugin>
</plugins>

Expected behavior

Should be Api containing @Validated generated

import org.springframework.validation.annotation.Validated;

@Validated
public interface DemoApi {
 ...
}

Currently @Validated annotation is missing.

Suggest a fix/enhancement

Add to api.mustache & apiController.mustache next line:

{{#useBeanValidation}}{{#performBeanValidation}}@Validated{{/performBeanValidation}}{{/useBeanValidation}}

Open api.mustache and apiController.mustache and review how useBeanValidation and performBeanValidation control generated annotations. Generate Spring Api and ApiController classes with both options enabled and verify that each includes the Validated import and annotation; confirm the annotation is absent when either option is disabled.