Changes in the pipeline configuration

1. Run Athena early testing only on merge request events and when changes in GeoModelCore, GeoModelIO or cmake directories, as well as in CMakeLists.txt
2. Run Ubuntu jobs only on merge request events when changes are either in CMakeLists.txt or any directory other than documentation
3. Run documentation building on merge request events when changes are in the documentation directory
4. Run documentation building and deployment after an MR has been merged