Implement benchmarker framework

[BenjaminPelletier]

This PR continues MVP work for #1566 by adding an implementation of the basic framework. The matplotlib figure generation is stubbed as well as the flight_planner virtual user, but otherwise the PR mostly implements the ability to run the example configuration. The execution hierarchy is roughly:

• benchmark.py (entrypoint)
  • engine/engine.py (main engine)
    • actions/actions.py (run before-load and after-load actions)
      • actions/run_command.py (action that runs a shell command)
    • loads/loads.py (run main load) plus loads/criteria.py (evaluation of completion criteria) plus status.py (status information for loads in general)
      • loads/user_ramp/user_ramp.py (user ramp load definition) plus loads/user_ramp/status.py (status information for the user_ramp load)
        • users/creation.py (means to create virtual users)
        • users/flight_planner/flight_planner.py (definition of virtual user that plans flights)
  • artifacts/generation.py (artifact generation)
    • artifacts/raw_report.py
    • artifacts/matplotlib/matplotlib_figure.py