DM-8889: Add detector z-offsets

[jmeyers314]

No description provided.

[RobertLuptonTheGood]

Looks good.

At the risk of attracting complaints about the general lack of docs on yamlCamera, where is it documented that offsets may be specified with 2- or 3- values (with [2] defaulting to 0)?

[jmeyers314]

where is it documented that offsets may be specified with 2- or 3- values (with [2] defaulting to 0)?

Added https://github.com/lsst/obs_lsst/pull/416/files#diff-a66f10959b31a508e4f363ab528d9c3e55f99de92d1c5ce8f14eabe266404d42R37-R39.

(Note that offsets here and elsewhere may
   either be specified as 2-tuples, in which case the z-offset is inferred to be
   0.0, or directly as 3-tuples with their z-offset explicit).