Changes in the pipeline configuration

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