Add pytest tests to stretch_core

[hello-chintan]

This PR adds tests to the stretch_core package using the launch_pytest framework. The idea is to verify that once nodes are launched the interfaces are active and performant. All topics are checked for existence and their publish rates. All services are checked if they are callable. All actions are checked if they exist and can be called at a specific rate

The stretch_core package tests the following nodes:

• stretch_driver - core topics, mode services and robot services
• detect_aruco - camera topics and aruco topics and detection rate
• d435i - camera topics and their rates
• rplidar - scan topic and its rate
• joint_trajectory_server - command rate for position and trajectory mode with smooth motion profiles

To test, use colcon test --packages-select stretch_core.

[hello-chintan]

Merged with deprecated branch iron by mistake! Merging into humble through this PR.

[binitshah]

Nice! I'm been meaning to write tests like these. Thank you for putting this together!!