Add poisson error on the dark to NIR reference files

[stscijgbot-jp]

Issue JP-3831 was created on JIRA by David Law:

JP-3463 added code support for including the Poisson error in the subtracted dark to the error stackup.  Thus far this has only been implemented for MIRI; this ticket is to study and (if appropriate) deliver such an update for the three NIR detectors as well.

[stscijgbot-jp]

Comment by David Law on JIRA:

ramperr.png attached shows earlier results for MIRI and NIRSpec