[JAVA] Generate JSON or YAML api specs from Maven plugin

Description

Actually we have to specify in Maven plugin "swagger-codegen-maven-plugin" an "inputSpec" value in plugin execution configuration. I didn't find a way to dynamically generate it from REST resources Spring class instead of a static file or an uri. It supposed that the server is already running to have the specs in v2/api-docs
It would be nice if we can build the server jar and the relative REST client jar.
So consumers of this REST API are always aware (in a SNAPSHOT case) of specs evolution on the server.

Swagger-codegen version

2.3.0

Suggest a fix/enhancement

Something like this could be useful in the server pom.xml, in an assembler profile for instance :

``

            <groupId>io.swagger</groupId>
            <artifactId>swagger-codegen-maven-plugin</artifactId>
            <version>${swagger.codegen.version}</version>
            <executions>
                <execution>
                    <goals>
                        <goal>generate</goal>
                    </goals>
                    <configuration>
                        <inputSpec>native</inputSpec>
                       <scanPackages>
                             <package>com.myproject.restdomain1</package>
                             <package>com.myproject.restdomain2</package>
                       <scanPackages>
                        <language>java</language>
                        <configOptions>
                            <sourceFolder>src/gen/java/main</sourceFolder>
                        </configOptions>
                    </configuration>
                </execution>
            </executions>
        </plugin>

Start by reviewing the swagger-codegen-maven-plugin configuration, its inputSpec handling, and the server pom.xml or assembler profile described in the issue. Determine whether the plugin can discover Spring REST resources and generate JSON or YAML specs during the build; done means the server and REST client jars can be built together without a static inputSpec or running server.