Add filename pattern for CLASS subscription files

[djhoese]

Replacement for #2156

• Closes AVHRR CLASS Filename prefix prevents reading with Scene. #2155
• Tests added
• Fully documented
• Add your name to AUTHORS.md if not there already

[codecov]

Codecov Report

Merging #2157 (795c977) into main (3718b65) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2157   +/-   ##
=======================================
  Coverage   93.95%   93.95%           
=======================================
  Files         285      285           
  Lines       43754    43754           
=======================================
  Hits        41108    41108           
  Misses       2646     2646           

Flag	Coverage Δ
behaviourtests	4.73% <0.00%> (ø)
unittests	94.62% <100.00%> (ø)

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Impacted Files	Coverage Δ
satpy/modifiers/parallax.py	99.15% <ø> (ø)
satpy/tests/reader_tests/test_aapp_l1b.py	100.00% <100.00%> (ø)
...atpy/tests/reader_tests/test_aapp_mhs_amsub_l1c.py	100.00% <100.00%> (ø)
satpy/tests/reader_tests/test_eps_l1b.py	100.00% <100.00%> (ø)
satpy/tests/reader_tests/test_sar_c_safe.py	100.00% <100.00%> (ø)
satpy/tests/writer_tests/test_ninjotiff.py	100.00% <100.00%> (ø)

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[coveralls]

Coverage remained the same at 94.571% when pulling 795c977 on djhoese:avhrr-class into 3718b65 on pytroll:main.

[mraspaud]

@djhoese I think we need to add @jeanlucshaw to the authors list, right?

[djhoese]

Yes. I'll add them.