Add logback-XSD project to Maven Central

[kdeenanauth]

When dealing with a lot of projects, it would be helpful if logback-XSD was made available via Maven Central. We could copy it to our projects via

<plugin>
  <!-- Used to pull logback.xsd from adk-core -->
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-dependency-plugin</artifactId>
  <executions>
    <execution>
      <id>unpack-logback-xsd</id>
      <phase>generate-sources</phase>
      <goals>
        <goal>unpack</goal>
      </goals>
      <configuration>
        <artifactItems>
          <artifactItem>
            <groupId>...</groupId>
            <artifactId>...</artifactId>
            <version>...</version>
          </artifactItem>
        </artifactItems>
        <includes>**/logback.xsd</includes>
        <outputDirectory>${project.basedir}/target/xsd-includes</outputDirectory>
      </configuration>
    </execution>
  </executions>
</plugin>