Change artifactId for the Maven plugin

The Maven plugin for Whisker currently has an artifactId of apache-whisker-plugin4maven, which does not follow the standard naming conventions for Maven plugins. The standard recommends <tool>-maven-plugin, where <tool> is the tool that is run through the plugin. In our case the correct artifactId would be apache-whisker-maven-plugin.

A hint that something is wrong can be seen by this warning in the build log:

[INFO] --- maven-plugin-plugin:3.3:descriptor (mojo-descriptor) @ apache-whisker-plugin4maven ---
[WARNING]

Goal prefix is specified as: 'plugin'. Maven currently expects it to be 'apache-whisker4'.

Somone has configured maven-plugin-plugin like this <goalPrefix>plugin</goalPrefix> which translated to this syntax when calling the Whisker Maven plugin from the command line:

mvn plugin:generate

which doesn't make any sense.