iceberg-kafka-connect-runtime fails with NoClassDefFoundError for org.apache.commons.configuration2.Configuration when used with Hadoop catalog

### Apache Iceberg version

None

### Query engine

None

### Please describe the bug 🐞

I’m trying to use the Kafka Connect Iceberg sink connector built from the latest main branch (v1.10.0-SNAPSHOT), following the instructions in the [iceberg-kafka-connect-runtime](https://github.com/apache/iceberg/tree/main/kafka-connect/kafka-connect-runtime) module.

After unzipping the built connector JARs into the Kafka Connect plugin path and starting a sink connector with type=hadoop catalog, the connector fails with the following error:

`java.lang.NoClassDefFoundError: org/apache/commons/configuration2/Configuration
at org.apache.hadoop.metrics2.lib.DefaultMetricsSystem.(DefaultMetricsSystem.java:43)
...
Caused by: java.lang.ClassNotFoundException: org.apache.commons.configuration2.Configuration
at org.apache.kafka.connect.runtime.isolation.PluginClassLoader.loadClass(PluginClassLoader.java:103)
`
and

`java.lang.NoClassDefFoundError: Could not initialize class org.apache.hadoop.security.UserGroupInformation
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:557)
...
`

**Steps to Reproduce**

1. Checkout https://github.com/apache/iceberg and build the connector by
./gradlew build -x test -x integrationTest

2. Copied the zip output from build/distributions/iceberg-kafka-connect-runtime-1.10.0-SNAPSHOT.zip to Kafka Connect plugin path and unzipped it.
3. Started the connector by submitting
`{
"name": "iceberg-sink",
"config": {
"connector.class": "org.apache.iceberg.connect.IcebergSinkConnector",
"tasks.max": "1",
"topics": "company.product.conc.level2",

"iceberg.catalog.name": "hadoop",
"iceberg.catalog.type": "hadoop",
"iceberg.catalog.warehouse": "s3a://domain/product/iceberg/",
"iceberg.catalog.hadoop.fs.s3a.endpoint": "<>:443",
"iceberg.catalog.hadoop.fs.s3a.access.key": "<>",
"iceberg.catalog.hadoop.fs.s3a.secret.key": "<>",
"iceberg.catalog.hadoop.fs.s3a.path.style.access": "<>",
"iceberg.catalog.hadoop.fs.s3a.impl": "org.apache.hadoop.fs.s3a.S3AFileSystem",

"flush.size": "500",
"key.converter": "org.apache.kafka.connect.storage.StringConverter",
"value.converter": "com.company.cdp.avroconverter.CustomAvroConverter",
"value.converter.avro.schema.file": "/etc/kafka-connect/data.avsc",
"value.converter.schemas.enable": "true",
"iceberg.tables": "db.processed_concentration",

"iceberg.table.schema.file": "/etc/kafka-connect/data.avsc"
}
}`
**Analysis**
It seems that the commons-configuration2 transitive dependency required by org.apache.hadoop.security.UserGroupInformation is not bundled into the connector distribution. Since Kafka Connect uses isolated classloading per plugin, these dependencies must be explicitly included.

**Suggested Fix**
Could we consider either:

Adding the missing commons-configuration2 dependency (and any other Hadoop transitive dependencies required at runtime) to the runtimeClasspath of iceberg-kafka-connect-runtime, or

Publishing a shaded uber-JAR (similar to how some other connectors are bundled), or

Updating documentation to guide users to manually include required Hadoop dependencies in the plugin path.

Please advise on the preferred direction. Happy to contribute a patch if needed.

### Willingness to contribute

- [ ] I can contribute a fix for this bug independently
- [ ] I would be willing to contribute a fix for this bug with guidance from the Iceberg community
- [ ] I cannot contribute a fix for this bug at this time

Start in the kafka-connect/kafka-connect-runtime module and inspect how its runtimeClasspath and distribution ZIP package Hadoop dependencies. Reproduce the failure using a Hadoop catalog and the reported connector configuration, then verify that the packaged connector starts without the commons-configuration2 NoClassDefFoundError or the subsequent UserGroupInformation initialization error.

Written by the indexing model from the issue text.