Add a useful error to users when running over xdigi files

Making an issue out of the mattermost conversation.

@amathad:

This is the 2nd time this sort of error has come up. xdigi cannot be used with FunTuple_Particles and also spruce cannot run over xdigi files. Wondering if the control flow can catch such type of things and throw a meaningful error to users.

@dfazzini :

yes I think that this can be quickly implemented in the DaVinci configuration.

@graven :

what can also be done (perhaps both should be done!) is to make the error message

Hlt2DecReportsDecoder_d044fa08        ERROR Hlt2DecReportsDecoder_d044fa08 :  No HltDecReports RawBank with sourceID 2 found

a bit more clear, and point out that 'not finding' this rawbank implies that the input file does not contain the a HltDecReport (in this case, for Hlt2)

FYI: @erodrigu and @sstahl . Tag @nskidmor as it is related to sprucing too.