decode OTEL_RESOURCE_ATTRIBUTES values

[brettmc]

per spec, resource attributes coming from environment should be decoded in the same way that they would be if coming from a header

Closes #786

[codecov]

Codecov Report

Merging #872 (888e298) into main (904da75) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 888e298 differs from pull request most recent head 0802700. Consider uploading reports for the commit 0802700 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #872   +/-   ##
=========================================
  Coverage     79.81%   79.82%           
- Complexity     2035     2036    +1     
=========================================
  Files           268      268           
  Lines          5271     5273    +2     
=========================================
+ Hits           4207     4209    +2     
  Misses         1064     1064           

Flag	Coverage Δ
7.4	79.31% <100.00%> (+<0.01%)	⬆️
8.0	79.81% <100.00%> (+<0.01%)	⬆️
8.1	79.95% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
src/Context/Context.php	82.05% <ø> (ø)
src/SDK/Resource/Detectors/Environment.php	100.00% <100.00%> (ø)

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