Write tutorial how to develop a real-time application

[JanStaschulat]

Write tuturial on https://docs.ros.org/en/rolling/Tutorials.html how to develop real-time applications with ROS 2. Including:

• Linux preempt_rt setup
• multi-threaded executor
• static executor
• cbg_executor
• assignment of priorities
• usage of ros2 tracing

Consolidate existing pages, e.g. on

• https://docs.ros.org/en/rolling/Concepts/About-Executors.html
• https://docs.ros.org/en/rolling/Tutorials/Building-Realtime-rt_preempt-kernel-for-ROS-2.html
• documentation availabe from ROS 2 Executor workshop

[carlossvg]

Related docs:

• https://docs.ros.org/en/rolling/Tutorials/Real-Time-Programming.html
• https://www.apex.ai/roscon-21

[JanStaschulat]

Action item:

• update and consolidate documentation