OARIS2 — sensor_plot_type structure changed

The Plot Reporting Use Case is confusing. For OARIS 1.1, the actual Plot structure was abstracted into a sub-type write_sensor_plot_type defined in Provide_Plots.idl. In OARIS 2.0, the IDL file Provide_Plots.idl has been removed, with the interface effectively reverting back to the OARIS 1.0 version with sensor_plot_type defined in Plot_Reporting.idl. Is this intentional or was an incorrect baseline used for creating OARIS 2.0? This may also explain why subsystem_id is also missing as per sensor_track_type.

Flattened Structure Is Intentional

This change is a consequence of applying the principal of flattening PIM methods with a single parameter consistently throughout the whole model when mapping to the DDS/IDL PSM (and also GraphQL).

The topic type for Plots should have been flattened in the same way as that for Tracks in v1.1. This has now been done for v2.0.