[incubator-kie-isssues-1139] Add support for xpath in conditional paths

[elguardian]

Closes apache/incubator-kie-issues#1139

[martinweiler]

LGTM @elguardian

[pefernan]

@elguardian From the engine side everything seems to work fine but I found an issue while testing the example in this PR inside a kogito app. Looks like there's a problem when generating the Kogito Persistence when the process variable type is org.w3c.dom.Document. The stack trace says:

java.lang.RuntimeException: io.quarkus.builder.BuildException: Build failure: Build failed due to errors
	[error]: Build step org.kie.kogito.quarkus.processes.deployment.ProcessesAssetsProcessor#postGenerationProcessing threw an exception: java.lang.RuntimeException: Error while generating proto for model class 
org.kie.kogito.hr.XPathProcessModel Custom type org.w3c.dom.Document is no supported by Kogito persistence, please consider using a class that extends java.io.Serializable and contains a no arg constructor

Additionally I couldn't make it work when the process uses a Pojo as variable, but I think we can fix this second scenario in a later improvement.

[elguardian]

@pefernan I will take care of the issue in the persistence stuff
apache/incubator-kie-issues#1204

[pefernan]

+1 Let's tackle the persistence in a new task.