Add support for NOAA-21 VIIRS

[adybbroe]

This PR adds support for the JPSS-2 (NOAA-21) VIIRS RSR data.
The actual pyspectral formattet hdf5 files are not yet uploaded to zenodo, so the version pointing to the RSR files remains as before. The RSR file version will be updated in another PR. See #155 and #157

• Closes #xxxx
• Tests added
• Tests passed: Passes pytest pyspectral
• Passes flake8 pyspectral
• Fully documented

[codecov]

Codecov Report

Merging #156 (5601501) into main (f0abf64) will not change coverage.
The diff coverage is n/a.

❗ Current head 5601501 differs from pull request most recent head 1017b40. Consider uploading reports for the commit 1017b40 to get more accurate results

@@           Coverage Diff           @@
##             main     #156   +/-   ##
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  Coverage   88.03%   88.03%           
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  Files          22       22           
  Lines        2473     2473           
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  Hits         2177     2177           
  Misses        296      296           

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unittests	88.03% <ø> (ø)

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[djhoese]

Now that #157 is done, does the URL in this PR need to be updated? Or does a new upload to zenodo need to happen?

[djhoese]

Really small cleanup comments, but otherwise looks good.

[adybbroe]

Now that #157 is done, does the URL in this PR need to be updated? Or does a new upload to zenodo need to happen?

I have already uploaded a new version with NOAA-6 and JPSS-2 updates to Zenodo a few days ago. But you are absolutely right the URL ought to be updated. I merge main into this one.