Avoid duplicating versionsMavenPluginRules.xml files

[kaklakariada]

PR generates a versionsMavenPluginRules.xml with the same content for each sub-module. We could avoid this by creating only one file in the root dir and reference it from the modules.

Idea: Add a property projectRootDir (or similar) to the generated parent pom and fill it with the relative path to the root dir. Then we can reference the file via

<rulesUri>file:///${projectRootDir}/versionsMavenPluginRules.xml</rulesUri>