Issue Description:

Getting started chapter contains only Rule Unit example

Acceptance Criteria:

• Add kie-drools-exec-model-archetype example to Getting Started Chapter
• Fix kie-drools-exec-model-archetype description to clarify it's not dedicated for Drools 7 : https://github.com/kiegroup/drools/blob/8.44.0.Final/kie-archetypes/kie-drools-exec-model-archetype/pom.xml#L14-L17
• Same fix for docs : https://github.com/kiegroup/drools/blob/8.44.0.Final/drools-docs/src/modules/ROOT/pages/getting-started/_first-rule-project.adoc?plain=1#L46-L49