Get plan status

[cartermak]

Add a plans status command which simply returns the status, comparable to the green "success" checkmark vs. yellow "modified" pencil, etc.

This should mirror the logic from the UI:

https://github.com/NASA-AMMOS/aerie-ui/blob/a15bda7f3f889c4372fe933dddaab68e81a0927b/src/stores/simulation.ts#L153-L172