Create DataModel for Dark monitors

[jwhite3]

The Dark Monitors will likely require the same (or very similar) bits of data to perform the actual monitoring, so it makes sense to create one DataModel for all of the dark monitors to use.

[jwhite3]

There seem to be a few options for doing this:

1. Create a DataModel that pulls corrtag files directly from the dark monitor programs. This would ensure that the data remains focused on what's needed for the dark monitors and is much more efficient than looking through all available corrtag files across all programs, but it also means that whatever list that defines the dark monitor programs would need to be updated yearly.

2. Create a CorrtagDataModel that's general to corrtag files, and then pull files with EXPTYPE = 'DARK'. This would avoid the issue of having to update the set of defined dark programs each year, but then there's the risk of the scope of this table becoming too large. There's currently no other monitor that requires data from corrtag files, so ingesting data from all COS corrtag files might be overkill.

3. Run through all new corrtag files, but only ingest if the EXPTYPE = "Dark". This is inefficient, but not prohibitively so, especially since there'd only be a need to run through all corrtag files one time (the first time), and then the monitor would only need to look at a few at a time after that (assuming that it executes every few weeks or so). This has the benefit of avoiding updating the dark programs list while also keeping the scope of the DataModel well-defined