User Story:
As a PSAP engineer, I want to simplify the notebook scale test codebase, so that it is easier to maintain.

Over the investigations on notebook scaling, the testing/notebooks directory got bloated with different functionalities that are not used anymore. We want to remove as many things as possible from there, without impacting the notebook gating test.

Additionally, the notebooks roles are currently stored in roles/rhods for historical reasons. We want to move them to roles/notebooks so that they are grouped more logically.