cesm_timeseries_generator.py needs to update the monthly average time coordinate for each variable

[bertinia]

Currently the history slice files and subsequent variable timeseries files reporting of the monthly
time average date is misleading to users because it writes the average value for the month at the
first time step of the subsequent month. Other models report the average value at the mid-point
of the month.

Kevin has a stand-alone serial tool that goes back and updates the files with the non-misleading time coordinate. This tool should be called from the cesm_timeseries_generator.py script as well.

[bertinia]

will need to be mindful of which variables should have this applied to them. The instantaneous variable will not need their times adjusted. So, we may need a list of variables for the tool.

There may be an ncks tool that does this (confirm with Gary or Dennis) but is it efficient?

Another option is to modify a python script that Kevin wrote.