Refactor modules structure of kogito-runtimes project

Soon, we should rethink the structure of top-level modules of the kogito-runtimes project to make it easier for anyone to understand it at first sight. 

Another aspect of refactoring is to make it easier for Google to find us, so the names of the modules should be meaningful. For example `jbpm` or `drools` or `kogito-serverless-workflow`. For example, we will be fairly visible in the search engine if someone searches for "kogito drools."

This is the new structure proposed by dzonca@redhat.com:

runtimes
addons
quarkus-integration
spring-integration
codegen
utils 

jBPM, Drools, Serverless Workflow modules should also be considered top-level elements.