KAFKA-19761 Gradle Shadow plugin version upgrade: 8.3.9 -->> 9.2.2

[dejan2609]

Prologue: #19513 (comment)

Release notes for Shadow plugin:

• https://gradleup.com/shadow/changes/#922-2025-09-26

I did some testing, and results look just fine ✅:

• gradle builds ./gradlew :jmh-benchmarks:shadowJar and ./gradlew releaseTarGz are successful
• generated distributions (kafka_2.13-4.2.0-SNAPSHOT-site-docs.tgz and
  and kafka_2.13-4.2.0-SNAPSHOT.tgz) have identical file numbers (for
  trunk and this branch)
• Kafka cluster starts and messages can be produced and consumed:
  https://kafka.apache.org/quickstart

⚠️ disclaimer notes:

• solution is generated via Gemini CLI
• Gemini prompt is based on Jira ticket (previously created by me):
  KAFKA-19761

[dejan2609]

@chia7712 Please review when you have some time.

[dejan2609]

I'll rebase this onto trunk (to include a new, updated Gradle version into this branch/PR).