Add use_center_grid_points namelist

[uramirez8707]

Description
Adds a new namelist, use_center_grid_points, which indicates whether or not to use the centroid values of the supergrid from the grid file as opposed to calculating it by taking the average of the four corner points. This is only relevant to OCN and ICE grids.

The namelist is needed because answers will not bit for bit reproduce, but overall the answers should not be very different.

The namelist should be set to .True.

Fixes #1537

How Has This Been Tested?
CI

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes

[bensonr]

lgtm