Replace derby examples with postgres

https://access.redhat.com/documentation/en-us/jboss_enterprise_application_platform_continuous_delivery/15/html-single/getting_started_with_jboss_eap_for_openshift_container_platform/index

There are three database examples in the documentation that use Derby database. Derby is unsupported for EAP and these examples should be replaced with a supported database, ideally postgres.

The locations:
3.3.1.1. Modules, Drivers, and Generic Deployments (two occurrences)
3.3.2.1. Datasources