Bump license-maven-plugin to 4.1 (from 1.9.0)

[brenuart]

The project is currently using com.mycila.maven-license-plugin:maven-license-plugin:1.9.0 which is a pretty old version of the plugin. The plugin is now at version 4.1 and with a different GAV. The correct GAV is now:

   <groupId>com.mycila</groupId>
   <artifactId>license-maven-plugin</artifactId>
   <version>4.1</version>

The plugin configuration should also be added to the section of the POM so it also applies when the plugin is invoked from the command line. This would allow to check and/or format the source files without requiring a "full" build as follows:

mvn license:check
mvn license:format

IMHO the build should only verify if a valid license is present on source files and fail if not. In other words, the build should invoke the "check" goal instead of "format" as it is for the moment. When it fails, the user can update the files by invoking the plugin on the command line as follows:

mvn license:format

(same behaviour as with checkstyle for instance, except checkstyle doesn't provide a goal to "fix" issues automatically)