Generate std Spectrum Products

[nkphysics]

Users doing spectrum analysis should be able to select an option to auto-generate the following for spectrum analysis through xspec:

• ni[OBSID].pha through xselect
• ni[OBSID].arf and arf_wt.lis
• ni[OBSID].rmf

[nkphysics]

This functionality will be added with the release of nicerl3 software roughly Oct 2022.
Thank you NICER team for making my life easier.

[nkphysics]

nicerl3-spect and nicerl3-lc tools were released with Heasoft v6.31 so the std products pipe lining will come from them. See docs below.

nicerl3-spect: https://heasarc.gsfc.nasa.gov/docs/nicer/analysis_threads/nicerl3-spect/
nicerl3-lc: https://heasarc.gsfc.nasa.gov/docs/nicer/analysis_threads/nicerl3-lc/