Kafka Connect: Include connector name in coordinator and committer thread names

### Apache Iceberg version

1.10.1 (latest release)

### Query engine

Kafka Connect

### Please describe the bug 🐞

## Problem
When multiple Iceberg sink connectors run in the same Kafka Connect worker process, all
coordinator threads share the same name `iceberg-coord` and all committer threads share
names like `iceberg-committer-0`, `iceberg-committer-1`, etc.
This makes log-based debugging difficult: when a coordinator fails to commit or a committer
thread throws an error, the log output gives no indication of which connector is responsible.

Including the connector name would greatly improve the log based debugging experience.

### Willingness to contribute

- [x] 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 sink connector code by locating where the coordinator and committer threads are created and named. Update the thread names so they identify their connector, then verify that logs from multiple connectors distinguish both coordinator and committer failures.

Written by the indexing model from the issue text.