Open-API: Replace shadow JAR with distribution plugin for REST fixture

[kevinjqliu]

Changes

• Replace shadow JAR with Gradle distribution plugin, modelled after
  kafka-connect-runtime. Uses installDist/distZip instead of shadowJar,
  producing a lib/ directory of individual JARs (66 JARs, 59MB total vs 201MB
  shadow JAR).
• Exclude cloud-specific thin modules (iceberg-aws, iceberg-gcp, iceberg-azure,
  iceberg-bigquery) and JUnit from the distribution. Cloud bundles are copied as
  separate shadow JARs in the Dockerfile.
• Update Dockerfile to use java -cp "lib/*" with the installDist output
  instead of java -jar with the shadow JAR. Remove EXPOSE since it is
  build-time metadata that cannot track runtime port overrides.
• Fix REST_PORT env var — renamed to CATALOG_REST_PORT so the server reads
  it through the CATALOG_* environment mapping convention.
• Add LICENSE, NOTICE, and runtime-deps.txt for the open-api distribution.
• Update CI workflow to build installDist plus cloud bundle shadowJar tasks.

Motivation

The shadow JAR bundled all transitive dependencies into a single 201MB JAR that was
unintentionally published to Maven Central.
Replacing it with individual JARs in a lib/ directory:

• Simplifies license compliance — each JAR retains its own META-INF/LICENSE
• Reduces build artifact size (201MB → 59MB)
• Follows the same pattern as kafka-connect-runtime
• Allows cloud bundles to be included/excluded independently

Testing

• ./gradlew :iceberg-open-api:installDist produces 66 JARs (no JUnit, no cloud thin modules)
• ./gradlew :iceberg-open-api:checkRuntimeDeps passes against baseline
• java -cp "lib/*" org.apache.iceberg.rest.RESTCatalogServer starts, /v1/config and
  /v1/namespaces respond correctly
• Docker image builds and passes healthcheck with full REST API functional

[kevinjqliu]

this is ready for first round of review.

Please take a look at build.gradle, .github/workflows/publish-iceberg-rest-fixture-docker.yml, docker/iceberg-rest-fixture/Dockerfile
and then open-api/runtime-deps.txt and runtime-deps.gradle

once those are good, please check open-api/LICENSE and open-api/NOTICE

[manuzhang]

I'm wondering whether we need all those jars and bundles for docker image and integration tests in iceberg-python and iceberg-rust.