[GEODE-10529] Update prepare_rc.sh to support Java 17

[JinwooHwang]

Summary

Updates prepare_rc.sh to support Java 17 for building Apache Geode 2.0.0 release candidates.

Changes

• Java Version Check: Updated from Java 8 (1.8) to Java 17
• Error Messages: Updated to reference JDK 17 and adoptium.net
• File Copying: Fixed geode-benchmarks to gracefully handle missing .travis.yml

Testing

Verified that the script correctly:

• Detects Java 17
• Rejects non-Java 17 versions
• Handles missing .travis.yml without failing

Related Issue

GEODE-10529

For all changes, please confirm:

• Is there a JIRA ticket associated with this PR? Is it referenced in the commit message?
• Has your PR been rebased against the latest commit within the target branch (typically develop)?
• Is your initial contribution a single, squashed commit?
• [ x] Does gradlew build run cleanly?
• Have you written or updated unit tests to verify your changes?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?

[JinwooHwang]

All checks have passed.