Replace Bitronix by Narayana and tomcat-dbcp in jBPm documentation

Current jBPM documentation mentions Bitronix on multiple places, including examples. As Bitronix has been replaced by Narayana and Tomcat DBCP, it should be reflected in the documentation.

For detail how to set up jBPM engine with Tomcat DBCP pooling data source, please see [1] and related classes in the same package.

[1] https://github.com/kiegroup/drools/blob/master/kie-test-util/src/main/java/org/kie/test/util/db/internal/PoolingDataSourceWrapperImpl.java