Match environment variables for config keys containing underscores

[thswlsqls]

Fixes #8932

Description

• ConfigUtil.getString normalized the lookup key with normalizePropertyKey (keeps _) but env var names with normalizeEnvironmentVariableKey (turns _ into .), so keys containing _ never matched an env var.
• So OTEL_EXPERIMENTAL_SDK_JVM_STACKTRACE=true was ignored, while the system property otel.experimental.sdk.jvm_stacktrace worked.
• Normalize the lookup key with normalizeEnvironmentVariableKey before comparing it with env var names. Keys without _ behave the same as before.
• System property matching and priority are unchanged.
• Updated the getString Javadoc to match.

Testing done

• Added a config_key assertion to ConfigUtilTest#getString_EnvironmentVariable (the build sets CONFIG_KEY=environment). It fails without the fix ("default") and passes with it.
• ./gradlew :common:check passed (9 tests).
• ./gradlew :sdk:common:test passed (346 tests).

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Waiting on reviewers · refreshed 2026-10-12 02:38 UTC

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.65%. Comparing base (387f5c5) to head (95ac981).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8933   +/-   ##
=========================================
  Coverage     90.65%   90.65%           
  Complexity    10887    10887           
=========================================
  Files          1015     1015           
  Lines         29731    29733    +2     
  Branches       3876     3876           
=========================================
+ Hits          26953    26955    +2     
  Misses         1860     1860           
  Partials        918      918           

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