`initialize_sponges_file` ignores default value of `USE_REGRIDDING` about mom6 HOT 2 CLOSED

This specific issue will be corrected once NOAA-GFDL#180 has been merged into main.

I have also created a test (in a separate commit) for any instances of calls to get_param without providing either a default value or a fail_if_missing argument, to avoid any other uninitialized variables. All code that is exercised by the MOM6-examples test suite (at https://github.com/NOAA-GFDL/MOM6-examples) are now passing these tests. However, I do not know whether this test is something that we will want to incorporate into our routine testing protocols, so for now I am keeping this new test on a separate branch at https://github.com/Hallberg-NOAA/MOM6/tree/fatal_missing_default,

from mom6.

The code correcting this issue has now been merged onto the main branch of MOM6 as a part of #1582, with the specific changes coming in from NOAA-GFDL#180.

from mom6.