Update Gradle Wrapper to 8.2.1 for Enhanced JDK20 Compatibility

[kaituo]

Description

• Upgraded to JDK20, making Gradle 7.6.1 incompatible. Reference: JDK20 migration
• Updated Gradle to 8.2.1 for JDK20 support. The gradle wrapper files are generated using the ./gradlew wrapper command.
• Upgraded nebula, mockito, bytebuddy, and spotless for JDK20 compatibility.
• Applied new formatting with updated spotless version.
• Replaced deprecated keywords in build.gradle:
  • archivePath -> archiveFile
  • archiveName -> archiveFileName
  • version -> archiveVersion
• Added test dependency on junit-platform-launcher as required by Gradle 8. Reference: Gradle 8.2.1 docs
• Removed outdated powermock (last new version in 2020) and refactored related tests.
• Adopted java { } configuration block due to Gradle 8 deprecations. Reference: Gradle 8.2.1 docs
• Removed org.junit.vintage dependency to resolve conflicts with Gradle 8's internal JARs. Also refactored related tests.
• Introduced gradle.properties for custom configurations, including build caching, parallel mode, and increased heap for tests.
• Added JDK20 to CI test environment.

Relevant PRs:

• Alerting#893

• opensearch-sdk-java#517

• Security PR

• Verification: Successfully verified the changes using gradle build.

Issues Resolved

#980

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Merging #985 (3117b1b) into main (5ac6390) will decrease coverage by 0.21%.
The diff coverage is 59.62%.

@@             Coverage Diff              @@
##               main     #985      +/-   ##
============================================
- Coverage     80.63%   80.42%   -0.21%     
+ Complexity     4590     4569      -21     
============================================
  Files           334      334              
  Lines         19104    19063      -41     
  Branches       1987     1987              
============================================
- Hits          15404    15331      -73     
- Misses         2755     2783      +28     
- Partials        945      949       +4     

Flag	Coverage Δ
plugin	80.42% <59.62%> (-0.21%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
.../java/org/opensearch/ad/AnomalyDetectorRunner.java	44.94% <0.00%> (+0.49%)	⬆️
...c/main/java/org/opensearch/ad/ml/ModelManager.java	83.52% <0.00%> (-1.00%)	⬇️
.../ad/rest/handler/ModelValidationActionHandler.java	0.00% <0.00%> (ø)
.../main/java/org/opensearch/ad/ml/CheckpointDao.java	71.80% <25.00%> (+0.05%)	⬆️
.../main/java/org/opensearch/ad/cluster/HashRing.java	82.18% <33.33%> (-0.48%)	⬇️
...a/org/opensearch/ad/indices/ADIndexManagement.java	81.25% <33.33%> (-3.13%)	⬇️
...java/org/opensearch/ad/task/ADBatchTaskRunner.java	81.20% <33.33%> (-4.22%)	⬇️
...arch/forecast/indices/ForecastIndexManagement.java	85.07% <33.33%> (-2.99%)	⬇️
.../handler/IndexAnomalyDetectorJobActionHandler.java	64.36% <37.50%> (+0.52%)	⬆️
...d/transport/GetAnomalyDetectorTransportAction.java	75.75% <50.00%> (+0.16%)	⬆️
... and 14 more

... and 7 files with indirect coverage changes

[dbwiddis]

LGTM!

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-985-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 4a09b741e1c127a92775cb55f4c56aa5c4f3f6a3
# Push it to GitHub
git push --set-upstream origin backport/backport-985-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-985-to-2.x.