Support redis-socket:// URLs when configuring a Redis client

[scottfrederick]

This is related to #21920.

Spring Data Redis has a RedisSocketConfiguration that can be used to configure a Unix domain socket connection to Redis. The Lettuce client supports domain socket configuration with URLs like redis-socket://redis/redis.sock.

If we decide to support redis-sentinel:// URLs in spring.redis.url, we might also want to support redis-socket:// URLs.

[snicoll]

Closing in favor of PR #27373