Update gradle wrapper to 8.14.4 to support Java 21

[ostinru]

I am not sure that I understand Gradle Compatibility Matrix[1]. However it seems that Gradle 8.x should work with java ranging from Java 8 to Java 21 well.

[1] https://docs.gradle.org/current/userguide/compatibility.html

[ostinru]

Hash sum from https://gradle.org/release-checksums/#8.14.4

[ostinru]

Run test suite with openjdk-21 here: ostinru#41
Looks ok

[ostinru]

Converting to draft - having issues running PXF on axiom-jre21 =/

[ostinru]

Tested with JDK 17, 21, 25 - at least it starts and can query Postgres datasources.

@leborchuk , this PR should remove blockers in supporting Rocky Linux 10.

[Copilot]

Pull request overview

This PR updates the server-side Gradle wrapper to a newer Gradle 8.x release in order to enable running builds with Java 21, and aligns related CI/container wiring with the new wrapper version.

Changes:

• Bump Gradle wrapper from 7.6.6 to 8.14.4 (including wrapper checksum file updates).
• Update CI Java matrix to include Java 21.
• Adjust build dependency management to pin Mockito/Byte Buddy versions for Java 21 compatibility.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
server/gradle/wrapper/gradle-wrapper.properties	Updates Gradle distribution URL + SHA256 to 8.14.4.
server/gradle/wrapper/gradle-8.14.4-wrapper.jar.sha256	Adds wrapper JAR checksum for the new Gradle version.
server/gradle/wrapper/gradle-7.6.6-wrapper.jar.sha256	Removes wrapper JAR checksum for the old Gradle version.
server/build.gradle	Updates plugins and adds dependencyManagement overrides intended for Java 21 support.
pom.xml	Updates RAT excludes to match the new wrapper checksum filename.
automation/src/main/resources/testcontainers/pxf-cbdb/Dockerfile	Updates container Gradle version and wrapper-cache warm-up steps.
.github/workflows/pxf-ci.yml	Adds Java 21 to the java-compatibility matrix.

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