Add lettuce Redis driver autoconfiguration.

[mp911de]

Introduce an alternative autoconfiguration if the lettuce Redis driver is available. Add lettuce-specific configuration property options spring.redis.lettuce.shutdown-timeout to control the shutdown timeout of the lettuce driver. Add documentation for the properties, the supported drivers, and how to switch between drivers.

Jedis stays the default driver even if both libraries are on the classpath.

[wilkinsona]

I think this requires a bit more thought (and possibly some breaking changes).

We currently have some spring.redis.pool.* properties that are ignored if you are using Lettuce. I think that's likely to confuse people. They should perhaps be moved to spring.redis.jedis.pool. What do you think @snicoll?

I am not keen on LettuceRedisProperties being mapped to a subset of the namespace that's already been claimed by RedisProperties. I think it would be preferable to follow the approach taken in ServerProperties so we'd have a RedisProperties.Lettuce inner-class similar to the ServerProperties.Tomcat inner class.

[snicoll]

I reacted with 👍 so maybe you didn't get the notification. Note also that jedis does require commons-pool2 so this would be a good thing to add this as an alternative (even though it does need Guava)

[mp911de]

Thanks for your feedback. I addressed your comments and pushed new commits, rebased to master.

[rwinch]

I would really like to see this support too. The lettuce driver uses multiplexing which reduces the overall connections to Redis. This means the lettuce driver works much better with Spring Session. In fact, the Pivotal CLA tooling switched to Lettuce due to larger number of connections causing alerting on our Redis instance.

[snicoll]

Moving to 2.0 as Lettuce 4.x requires Java8

[snicoll]

This PR will be reworked by @mp911de once breaking changes in Kay have landed on master

[snicoll]

Thank you so much @mp911de!