Need to track multiple cobra configurations

As discussed in DAMD-32 and DAMD-42, there are two files that describe the mapping from targets to cobras, currently called pfiDesign and pfsConfig.  We need to track these in the operational database, as we may create multiple pfsConfigs from the same pfiDesign (e.g. in different months).

We also need to track the fact that multiple target lists will result in more than one pfiDesign due to the instrument rotator.  Different targets may also appear in multiple pfiDesign files, depending on how we carry out the survey.

This book-keeping is not currently carried out by the pipeline and is not described in the data model, but we will need to generate lists of visits to be reduced for given targets on the sky, and this information will be needed then.