CI: add nightly scheduled execution, perform selective test execution upon targeted platform changes

[jamoralp]

As the micro_ros_setup keeps growing and adding new features, so it does its continuous integration system.

This leds to CI executions taking too much time and often slowing the development process. Therefore, two enhancements are proposed:

• Perform a nightly CI execution, every 24 hours, where all the tests will be run.
• Based upon the platform (host, freertos...) in which the changes are taking place, run only those tests affected by these changes. This can be easily achieved thanks to this repo's folder structure.