change file template for RTMA skewTs

[christinaholtNOAA]

------ May 10

This work is likely in the regional_workflow and should be handled as a development to that repository. We will need to get more information from Guoqing about which RTMA this is, and whether the name of the file has already changed. It must be in place for us to make that change.

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From Guoqing (via Slack), 19 April:
Hi the graphic team, currently the python graphic try to look for the bgrd3d files:
python -u /lfs/3DRTMA/RTMA/python_graphics/create_graphics.py skewts -a 3 -d /scratch2/results/rtma.v0.4.0/prod/RTMA_CONUS.20230414/14/ -f 0 0 --file_tmpl 'RTMA_CONUS.t14z.bgrd3df{FCST_TIME:03d}.tm00.grib2' --file_type nat ....

I think in the long run, we will eventually use the original "rtma.t14z.natlev.f000.conus_3km.grib2" naming convention (which is the actual operational naming). I would suggest making this change when possible. Thanks!