kie-soup-dataset-elasticsearch pom.xml is not XSD-valid

Maven repository validation found that org.kie.soup:kie-soup-dataset-elasticsearch pom.xml is invalid according to Maven pom XSD [1].

The validation error is the following:

cvc-complex-type.3.2.2: Attribute 'combine.self' is not allowed to appear in element 'configuration'.

When inspecting [1], it indeed allows the ``combine`` attribute in children of the ``configuration`` element, but not in the ``configuration`` element itself. It is also mentioned in the documentation:

You can control how child POMs inherit configuration from parent POMs by adding combine.children or combine.self attributes to the children of the configuration element:
...

I have tried to move the attribute to relevant children and the resulting pom.xml is valid. For quick validation, this tool [2] can be used: [3] shows an example of the violation, [4] shows a proposed fix.

[1] http://maven.apache.org/xsd/maven-4.0.0.xsd
[2] http://www.utilities-online.info/xsdvalidation
[3] http://www.utilities-online.info/xsdvalidation/?save=8841bd79-fa6f-4303-80b3-4f31930b2fb8-xsdvalidation
[4] http://www.utilities-online.info/xsdvalidation/?save=8c7d61c9-d4d6-4ef6-932b-8d6a295a266f-xsdvalidation