Fix automatic reader table not listing readers with missing dependencies

[BENR0]

This makes a minor modification to the available_readers function to be able to pass a yaml loader type.
Based on this for reader table generation when BasicLoader is passed reader classes are not instantiated and thus readers with missing dependencies in the RTD build environment are now included in the reader table.

• Closes Supported readers page does not include many readers #2189

[mraspaud]

@BENR0 don't worry about the linting error, I have fixed it in my PR, which I will merge as soon as the tests pass

[mraspaud]

Thanks for the quick fix, any chance of adding a test?

[codecov]

Codecov Report

Merging #2191 (3406026) into main (acd0745) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2191      +/-   ##
==========================================
+ Coverage   94.03%   94.04%   +0.01%     
==========================================
  Files         289      289              
  Lines       44564    44617      +53     
==========================================
+ Hits        41904    41960      +56     
+ Misses       2660     2657       -3     

Flag	Coverage Δ
behaviourtests	4.72% <25.80%> (-0.03%)	⬇️
unittests	94.70% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/composites/config_loader.py	94.11% <100.00%> (+0.95%)	⬆️
satpy/plugin_base.py	95.45% <100.00%> (+7.45%)	⬆️
satpy/readers/__init__.py	98.22% <100.00%> (+0.68%)	⬆️
satpy/readers/yaml_reader.py	97.50% <100.00%> (+0.22%)	⬆️
satpy/tests/test_readers.py	98.95% <100.00%> (+0.04%)	⬆️
satpy/utils.py	24.69% <100.00%> (-0.31%)	⬇️
satpy/writers/__init__.py	88.96% <100.00%> (+0.37%)	⬆️
satpy/tests/reader_tests/test_hrit_base.py	96.55% <0.00%> (-1.67%)	⬇️
satpy/readers/utils.py	91.95% <0.00%> (-0.39%)	⬇️
satpy/readers/hrit_base.py	82.87% <0.00%> (-0.19%)	⬇️
... and 7 more

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[coveralls]

Coverage increased (+0.01%) to 94.651% when pulling 3406026 on BENR0:fix_doc_reader_table into acd0745 on pytroll:main.

[djhoese]

So what's left on this? I think @mraspaud was hoping for some type of test?

[BENR0]

@mraspaud @djhoese I added the test.

[djhoese]

One small request