Explicitly set the java toolchain and release version

[adwsingh]

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Describe your changes

Without these settings, the Java version declared in Gradle module metadata depends on whatever JAVA_HOME happens to be set on the release machine. This affects consumers that use Gradle's JVM version compatibility checking during dependency resolution.

For example, s3 version 1.0.16 declares org.gradle.jvm.version: 25, which breaks consumers like smithy-java that run on JDK 21. Version 1.0.17 declares JDK 17, presumably because the release host had a different JAVA_HOME. Since these jars only contain Smithy JSON models and no bytecode, the declared JVM version is irrelevant to actual compatibility but Gradle enforces it regardless. I changed it to 8 to maximize compatibility.

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• I have read the Contributing Guidelines.
• I confirm that this pull request is not against the generated models.
• My contribution is licensed under the Apache-2.0 license.