DataSet Definition auto detect datasource from persistence.xml

Right now the datasource is hardcoded into the DashbuilderBootstap classes with the dataset definitions. We should be able to auto detect the data source deflation from the persistence.xml. Here are some links of where the datasource is hardcoded:
https://github.com/droolsjbpm/jbpm-console-ng/blob/master/jbpm-console-ng-showcase/src/main/java/org/jbpm/console/ng/server/impl/DashbuilderBootstrap.java#L32

https://github.com/droolsjbpm/kie-wb-distributions/blob/master/kie-wb/kie-wb-webapp/src/main/java/org/kie/workbench/backend/DashbuilderBootstrap.java#L32