Use org.graalvm.buildtools:native-maven-plugin as plugin for native builds

[obfischer]

It seems so, that the current way to build native images is by using org.graalvm.buildtools:native-maven-plugin. Therefore we should used this plugin instead of org.graalvm.nativeimage:native-image-maven-plugin.

The switch should be done after the release of the first productive version of the SemVer commandline client.