Document new kie-server persistence feature

This commit
https://github.com/kiegroup/droolsjbpm-integration/commit/cf08c33f8136d3899d0d4ce02d32b35c97218d59

introduced new feature.

It is now possible configure kie-server persistence with finer detail, by passing hibernate/jpa parameters as system properties.

kie-server will take properties with following prefix into consideration:

• javax.persistence
• hibernate

This allows you to override default persistence.xml settings of kie-server in very elegant way.

Here is an example of valid config for JBoss:

<system-properties>
    ...
        <property name="hibernate.hbm2ddl.auto" value="create-drop"/>
    ...
<system-properties>

This means that after every restart, kie-server's database will be dropped (losing all the data) and created again empty (this is suitable for early dev)

Doc preview: RHPAM-I. Managing and monitoring KIE Server

View changes: Pull request

Doc impact: Please check 18.1. Configuring KIE Server Persistence from RHPAM doc.