Add new file to reformat OM4 data

[surbhigoel77]

The PR focuses on reformatting the OM4 masking file called wetmask and making it compatible to current eval code. Current eval code uses DINO masking variables like e1t * e2t instead of OM4's areacello. It has separate masks for variables like tmask, umask, vmask, fmask. Whereas, OM4 only has one mask wetmask

• Provide documentation for guidance

This will close #83