Toolbox mvnsh integration

[cstamas]

Integrate Toolbox into mvnsh.

Example:
https://gist.github.com/cstamas/81b150e3f4b8347f0610779f4f230421

Use it as following entry in .mvn/extensions.xml:

<?xml version="1.0" encoding="UTF-8"?>
<extensions>
    <extension>
        <groupId>eu.maveniverse.maven.toolbox</groupId>
        <artifactId>mvnsh</artifactId>
        <version>0.6.2-SNAPSHOT</version>
    </extension>
</extensions>

Needs Maven 4.0.0-rc-3+