Currently metadata associated with exposures is accessed in a few different ways: through the Calib object, through the Wcs object, and through the metadata object.
In conjunction with
DM-5502, which is to figure out what metadata is needed, this will provide a single interface to exposure oriented metadata. One tricky thing is that the Calib object has some subset of the metadata we'll need in a sanitized form, but we won't want to have to remember where to look for metadata. If we can't extend the Calib object to hold all sanitized metadata, we should create a new metadata object to store all sanitized metadata and remove the pieces from Calib that are currently there.