Add Redis Streams event queue provider

## Summary

Conductor currently supports SQS, AMQP, and NATS as event queue providers but lacks a Redis Streams option. Since Redis is already the default persistence backend, a Redis Streams event queue would reduce infrastructure dependencies for many deployments.

## Desired Behavior

New `redis-event-queue` module providing:

- `RedisObservableQueue` — core implementation using XREADGROUP/XACK with Lettuce client
- `RedisEventQueueProvider` — queue factory with caching
- `RedisEventQueueConfiguration` — Spring Boot auto-configuration
- Dead letter queue (DLQ) support via separate stream
- Consumer group-based reliable messaging

Configuration prefix: `conductor.event-queues.redis.*`

## Prior Art

Community PR #700 by @mfechtner implemented a complete module (1130 additions) including configuration, tests, and Docker config.

Start by reviewing the existing SQS, AMQP, and NATS event-queue providers, then compare them with community PR #700. The new redis-event-queue module should cover RedisObservableQueue, RedisEventQueueProvider, RedisEventQueueConfiguration, consumer groups, XREADGROUP/XACK handling, a separate DLQ stream, caching, tests, and Docker configuration.

Written by the indexing model from the issue text.