Loading detector data without `detector_number` using application definitions

[nvaytet]

The Orca data (TBL & Odin) has no detector_number.

We can wait for ECDC to add them in, but they anyway seem reluctant to then specify the axes attribute on the NXdetector which would allow us to determine the dimensions of the data.

Instead, can we use scippnexus's application definitions to customize the loading and fix the missing fields on-the-fly? It should be predictable enough that we want to always do the same thing?