Column sdtype is so useful it should become part of RDR2

[michaelaye]

This column indicates into what category I have put the data from an l1a file.
Writing this out into the RDR2 file could help find bugs in my code at a later stage and could help someone with doing deep diagnostics.
The types are as follows:

Datatype	sdtype value
science data	0
space view	1
blackbody view	2
solar target view	3
stowed	-2
moving	-1