Match environment variables for underscore keys in DefaultConfigProperties

[thswlsqls]

Related to #8932. Follow-up to #8933, which fixes the same mismatch in ConfigUtil.getString.

Description

• DefaultConfigProperties stored environment variable keys with _ replaced by ., but kept _ for all other keys and lookups.
• So OTEL_JAVA_EXPORTER_MEMORY_MODE was ignored: stored as otel.java.exporter.memory.mode, looked up as otel.java.exporter.memory_mode.
• Normalize every stored and looked-up key the same way (lower case, - and _ replaced with .), and update the class Javadoc. Keys without _ behave as before.
• All sources now write to the same key, so the documented priority holds: system properties over environment variables over defaultProperties, with withOverrides on top.
• a_b and a.b now map to the same key, as environment variables already did.

Testing done

• Added three ConfigPropertiesTest cases with OTEL_JAVA_EXPORTER_MEMORY_MODE=immutable_data set in the module's test task: env var only, env var over default, system property over env var.
• The first two fail without the fix (null and "reusable_data").
• ./gradlew :sdk-extensions:autoconfigure-spi:check passed (19 tests).
• ./gradlew :sdk-extensions:autoconfigure:check :exporters:otlp:all:test passed (198 and 117 tests).

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Waiting on the author · refreshed 2026-10-17 02:30 UTC

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.65%. Comparing base (4662b08) to head (53b050c).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8951      +/-   ##
============================================
+ Coverage     90.61%   90.65%   +0.04%     
- Complexity    10882    10889       +7     
============================================
  Files          1015     1015              
  Lines         29731    29731              
  Branches       3876     3876              
============================================
+ Hits          26942    26954      +12     
+ Misses         1872     1860      -12     
  Partials        917      917              

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