'g.measurement.InternalKey' missing from the iMS100 GDP

**Describe the bug**
In a campaign setting, custom flight IDs (e.g. `F07`) are defined before GRUAN flight IDs are minted. They are also easier to use to reference specific campaign flights.

However, dvas relies on the GRUAN Measurement ID to tell flights apart. In order to automatically tie these to custom campaign IDs, dvas could make use of 'g.measurement.InternalKey' (assuming these get filled with appropriate info at the GDP creation) to correctly associate GDPs to flights.

Unfortunately, this field is present in the RS41 GDP, but not the iMS100 GDP. Until this becomes the case, an external file linking campaign flight IDs to GRUAN IDs will be required by dvas.