MARBL_TRACERS_IC_FILE for the new grid

[alperaltuntas]

When a MARBL compset is run with the new grid (t233), we get an error indicating that MARBL_TRACERS_IC_FILE doesn't exists.

We probably want to place MARBL_TRACERS_IC_FILE under grid_indpt so that it gets shared by both t232 and t233.

However, I am not sure if MARBL_TRACERS_IC_FILE can accept absolute paths. If it can't, then we'll need a code change to allow that.

[alperaltuntas]

And this probably applies to other MARBL input files too.

[mnlevy1981]

I think there are three files to update:

1. The tracer IC file, which definitely belongs in ocn/mom/grd_indpt
2. The river nutrient flux file, which I have created for tx2_3v3 already but still need to test
3. The iron sediment and vent flux files, which I have not created for tx2_3v3 yet

I am trying to document steps [2] and [3] so that the process can be included in NCAR/tx2_3 (see NCAR/tx2_3#15), and [3] is fairly complicated. Once all the files exist, I'll create a MOM_interface branch to update MOM_input.yaml and input_data_list.yaml