Improve scheduling configuration of examples_rclcpp_cbg_executor package

[ralph-lange]

Chose the configuration of the high prio Executor thread to be below typical threaded interrupt handlers. Explained scheduling configuration in the code.

[adityapande-1995]

CI :

• Linux
• Linux-aarch64
• Windows

[adityapande-1995]

A small question : why are we changing the existing scheduling priority in this example ? Was that causing some problems, or this is just an enhancement ? cc @wjwwood

[ralph-lange]

The motivation of changing the priorities was to have a more realistic example. In Linux, interrupt threads often get priority 50, i.e., exactly (sched_get_priority_min(SCHED_FIFO) + sched_get_priority_max(SCHED_FIFO)) / 2.

I expect that in most real-world ROS-based application, priorities below this value are sufficient. The original priority of sched_get_priority_max(SCHED_FIFO) for the high-priority thread in this example is completely exaggerated, cf. my talk at last year's ROS World workshop on execution management (video, slides).

Please note that I implemented the examples_rclcpp_cbg_executor package, i.e., I'm correcting myself with this PR :-)

[adityapande-1995]

Thanks for the clarification !