Improve workflow_engine info message "Executing tasks in parallel"

[mhamra]

Target version	Related issue	Related PR/dev branch
TBD	#5220

The workflow_engine sends the message "Executing tasks in parallel". I recommend to change this message to this:

f"Executing workflow tasks with thread pool count: {threads}".

I also recommend renaming the method WorkflowProcesor.execute_tasks_parallel to WorkflowProcesor.exectue_tasks