Docs: Feedback for Threading Model

Hi, I have some feedback about [this page](https://github.com/hazelcast/imdg-docs/edit/v/3.12/docs/modules/performance/pages/threading-model.adoc)

Can it be explicitly state which operations use partition threads and which use generic threads?

The only examples are:

- operations that are aware of a certain partition, e.g., IMap.get(key)
- operations that are not partition aware, e.g., IExecutorService.executeOnMember(command, member)

So the assumption all operations on IMap are partition threaded and all ExecutorService operations are generic threaded.

I've had to work it out by trial and error, so would be handy for it to just be explained.