Add Util Direcotry for HDASApp

[JingCheng-NOAA]

Inspired by the discussion related to pressure analysis in fv3jedi, GDASApp has a util to store applications such ass AddIncrement to compute analysis offline and variable change on the state. It would be nice for HDASApp to have a similar subdirectory to store such tools.

[JingCheng-NOAA]

A subdirectory utils adopted from GDASApp has been included in HDASApp, https://github.com/NOAA-EMC/HDASApp/tree/add_util. Rest work is to figure out the appropriate yaml file that can work with this function