disallow non-standard boolean config values

[brettmc]

per spec, only 'true' and 'false' are valid boolean values. anything else should be interpreted as false and a warning emitted.

Closes #861

[codecov]

Codecov Report

Merging #870 (5f4753e) into main (904da75) will decrease coverage by 0.08%.
The diff coverage is 70.00%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #870      +/-   ##
============================================
- Coverage     79.81%   79.73%   -0.09%     
- Complexity     2035     2036       +1     
============================================
  Files           268      268              
  Lines          5271     5274       +3     
============================================
- Hits           4207     4205       -2     
- Misses         1064     1069       +5     

Flag	Coverage Δ
7.4	79.22% <70.00%> (-0.09%)	⬇️
8.0	79.72% <70.00%> (-0.09%)	⬇️
8.1	79.86% <70.00%> (-0.09%)	⬇️

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

Impacted Files	Coverage Δ
src/SDK/Common/Configuration/Configuration.php	95.23% <62.50%> (-4.77%)	⬇️
.../SDK/Common/Configuration/Parser/BooleanParser.php	88.88% <100.00%> (ø)
src/SDK/SdkAutoloader.php	34.78% <0.00%> (-8.70%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 904da75...5f4753e. Read the comment docs.