Expand restart frequency options beyond hourly and monthly

[barlage]

Expected Behavior

Add restart frequency options:

1. output restarts at just the final time of the run
2. output restarts at specified times
3. output no restarts

Current Behavior

2 options: restarts output monthly or every restart_frequency_hours hours

Possible Solution

pack into the non-positive number approach used for monthly, i.e. 0=none, -1=monthly, -2=end of run (or something like that).

add a vector to namelist.hrldas of date strings or hours (this would be easier) when restarts are requested