Infra: Add retry mechanism for gradle commands in CI

[ebyhr]

CI occasionally fails with Could not resolve ... Received status code 403 from server when Maven Central has a transient issue.

https://github.com/apache/iceberg/actions/runs/37177308257/job/111362510376?pr=18362

> Could not resolve all files for configuration ':iceberg-spark:iceberg-spark-3.5_2.12:compileClasspath'.
   > Could not resolve at.yawk.lz4:lz4-java:1.12.0.
     Required by:
         project :iceberg-spark:iceberg-spark-3.5_2.12 > org.apache.spark:spark-hive_2.12:3.5.9 > org.apache.spark:spark-core_2.12:3.5.9
      > Could not resolve at.yawk.lz4:lz4-java:1.12.0.
         > Could not get resource 'https://repo.maven.apache.org/maven2/at/yawk/lz4/lz4-java/1.12.0/lz4-java-1.12.0.pom'.
            > Could not GET 'https://repo.maven.apache.org/maven2/at/yawk/lz4/lz4-java/1.12.0/lz4-java-1.12.0.pom'. Received status code 403 from server: Forbidden

This PR adds .github/bin/retry script, which is similar to the script used in Trino.

Not touched:

• publish-snapshot.yml: publishes to Nexus, not read-only
• source-release-ci.yml: gradle runs in a copied working directory; the script's relative path won't resolve there