Adding option to read ice thicknesses

[kshedstrom]

• The default ice thicknesses are somewhat thin. Matt Harrison and Mitch Bushuk and I had talked about a desire to try other thickness distributions.

[marshallward]

Gaea regression: https://gitlab.gfdl.noaa.gov/ogrp/SIS2/-/pipelines/21085 :heavy_check_mark: :yellow_circle: