Add Redis Sentinel support and local integration tests for ebean-redis

[leehaut]

• Add Redis Sentinel deployment mode to ebean-redis, while keeping standalone as the default (fully backward compatible).
• Generalize Redis connectivity from JedisPool to Pool<Jedis> so both standalone and sentinel pools work with existing cache and pub/sub logic.
• Add optional local integration tests that run against a real Redis instance configured via redis-local.yml.
• Guard against NPE when L2 table-modification messages arrive before createCacheNotify() registers a listener.