wave_elevation_spectrum exported for CICE6 is not updated at coupling frequency

[DeniseWorthen]

Describe the bug
The wave_elevation_spectrum exported by the mesh cap (dev/ufs-weather-model branch) is not updated at the wave-ice coupling frequency.

To Reproduce
Enable wave-cice6 coupling and examine the coupler history file output. Currently the export field is filled w/ the value calculated in w3outg. The exported fields will therefore be updated only at the output frequency.

Expected behavior
The exported wave_elevation_spectrum should be updated at each coupling frequency.

Screenshots
The following figure shows a single point location and frequency for the exported wave_elevation_spectrum (coupling frequency = 720s) as well as the same field in the wave output file (frequency=3600s). The upper panel is the current behaviour; the lower panel shows the correct behavior. The fix is to add a routine to calculate the wave_elevation_spectrum at the required frequency w/in the wav_import_export module.