Fix Config.logLevel precedence and javadoc

[gabrielfeo]

Fix precedence of Config.logLevel sources so that environment variable is always preferred. Also fix #284.

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Generated API diff

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Job Summary for Gradle

Check PR :: kotlin-tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
develocity-api-kotlin	test compileIntegrationTestKotlin :build-logic:check	8.8	❌

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Job Summary for Gradle

Check PR :: build-javadoc

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
develocity-api-kotlin	dokkaHtml	8.8	❌