[uss_qualifier/scd] Add 'Down USS' scenario; SCD0005 requirement validation

[mickmis]

This also adds some things we need:

• additional functions to query the DSS
• utility function to extract generically an error message from a query response
• generic test steps to change availability of an USS

[BenjaminPelletier]

Thanks, this looks great! I do think we want to make sure the code works as part of the PR, but this can be easily accomplished (I did so locally) by adding something like this section before the aggregate checks in the f3548_21 test suite:

- action_generator:
    generator_type: action_generators.flight_planning.FlightPlannerCombinations
    resources:
      flight_planners: flight_planners
      conflicting_flights: conflicting_flights
      dss: dss
    specification:
      flight_planners_source: flight_planners
      roles:
        - tested_uss
      action_to_repeat:
        test_scenario:
          scenario_type: scenarios.astm.utm.off_nominal_planning.down_uss.DownUSS
          resources:
            tested_uss: tested_uss
            dss: dss
            flight_intents: conflicting_flights
        on_failure: Continue
  on_failure: Continue

[mickmis]

Thanks, this looks great! I do think we want to make sure the code works as part of the PR, but this can be easily accomplished (I did so locally) by adding something like this section before the aggregate checks in the f3548_21 test suite:

Of course! Forgot to include it. I had it locally and the test ran fine. Updating now.