Generate ICs for pot_temp, frazil, ocean_age_tracer

[aekiss]

To support cold starts with these changes COSIMA/01deg_jra55_iaf@96876c6 we need to make three new files:

• ocean_pot_temp.res.nc defining pot_temp based on WOA13v2 for consistency with conservative temp initial condition
• ocean_frazil.res.nc defining zero frazil initial condition
• ocean_age.res.nc defining zero ocean_age_tracer initial condition

See /g/data/ik11/restarts/access-om2-01/01deg_jra55v140_iaf/restart243/ocean for examples (though we'd want to fill in the land points).

See mom-ocean/MOM5#339 and COSIMA/access-om2#235

[aekiss]

Once the initial conditions are available the necessary field_table changes can be cherry-picked from the fix-tracer-init branch into the master and master+bgc branches for each of the 6 standard configs.