Add GEN0405 checks

[BenjaminPelletier]

Is your feature request related to a problem? Please describe.
Currently, we do not have test coverage for GEN0405 (user notifications upon operational intent state changes).

Describe the solution you'd like
Once the user notifications query in the flight_planning API is available, we can verify GEN0405 compliance by adding a user notification query after an operational intent state change is made. We can limit results to notifications occurring after the action taken by uss_qualifier to cause the state change. We should not count notifications indicating conflicts unless the state change resulted in a conflict.

The documentation of this scenario can be developed before the final version of the API update is merged since the design doc already provides a good description of what it will accomplish, and there is already a PR with a draft that hasn't collected any additional comments currently.

To maximize backwards compatibility, our implementation should be resilient to encountering 404 upon querying user notifications and gracefully skip the GEN0405 checks in that case.