improve MOM6 parameter file support

[aekiss]

It would be good to have more complete support for MOM6 parameter files.

93b3161 adds some support, but should also

• support #override
• hide &mom6 in outputs
• fix (or at least disable) --tidy_overwrite for MOM6 parameter files

[aekiss]

also see what's done in https://github.com/micaeljtoliveira/om3utils/blob/main/om3utils/mom6_input.py