Able to configure thread pool queue size in execution server

When we execute Planner in kie-server, ThreadPoolExecutor is used and its max pool size and queue size are determined by availableProcessorCount minus 2.

https://github.com/kiegroup/droolsjbpm-integration/blob/7.23.x/kie-server-parent/kie-server-services/kie-server-services-optaplanner/src/main/java/org/kie/server/services/optaplanner/OptaplannerKieServerExtension.java#L86-L96

It's understandable that we leave 2 cores for other functionalities so max pool size is fine.

However, this JIRA requests to be able to configure "queue size" (e.g. by system property) as it doesn't directly impact on CPU.