Use ServiceLoader for ExpressionHandler implementations

Instead of using class instantiation we should use ServiceLoader as it fits better with Quarkus.

Example implementation: ObjectMarshallerStrategy

https://github.com/kiegroup/kogito-runtimes/blob/main/jbpm/process-serialization-protobuf/src/main/resources/META-INF/services/org.kie.kogito.serialization.process.ObjectMarshallerStrategy 

https://github.com/kiegroup/kogito-runtimes/blob/main/quarkus/extensions/kogito-quarkus-processes-extension/kogito-quarkus-processes-deployment/src/main/java/org/kie/kogito/quarkus/processes/deployment/ProcessesAssetsProcessor.java#L125