diag_manager writing a default fill value when there is no data

[thomas-robinson]

Is your feature request related to a problem? Please describe.
The diag_manager outputs a NETCDF default fill value if a buffer is to be written without being initialized. The buffer is initialized with this value. This happens when running a GFDL model for 0 days.

Describe the solution you'd like
Up for debate is what should happen in the case. Should there be no file? If the missing_value attribute is added, should the array be filled with the missing_value specified in the code? If _fillvalue is defined, should it use that value?

Describe alternatives you've considered

Additional context

[thomas-robinson]

@uramirez8707 We were just talking about this. Let's put it on the agenda for the next FMS meeting

[thomas-robinson]

In the new diag manager, we will open the file when it's time to write (has data to write) and write the meta data at the first open. This is a change in behavior that needs to be documented clearly.

[uramirez8707]

Fixed in #1505
See documentation for more details