Change the suffix to the input IMS data

[jiaruidong2017]

Update the input file suffixes from .asc to .dat, including those for ASCII and NetCDF formats.

Contributes to NOAA-EMC/GDASApp#2023

[ClaraDraper-NOAA]

I'd prefer to keep the original suffix to make it easier to trace the filetype, but I see that this is consistent with the IMS proc code testing the file type, so I'll defer to how @CoryMartin-NOAA would like to handle it.

[CoryMartin-NOAA]

What is the suffix of the file in the dump directory? Is it asc? I would also prefer it to be reflective of what the format is.

[jiaruidong2017]

What is the suffix of the file in the dump directory? Is it asc? I would also prefer it to be reflective of what the format is.

The ASCII file in dump directory uses the .asc extension. For reanalysis project, they prefer to use NetCDF format with the .nc extension.

[CoryMartin-NOAA]

Ok so lets either do something like:

input scf file: './obs/ims{{ snow_background_time_julian }}_4km_v1.3{ims_snow_suffix}'

or

{% if use_ims_nc %}
input scf file: './/obs/ims{{ snow_background_time_julian }}_4km_v1.3.nc'
{% else if %}
input scf file: './/obs/ims{{ snow_background_time_julian }}_4km_v1.3.asc'
{% end if %}

The top one will be easier to implement