Apply non-blocking eviction when using Lettuce for RedisCache.

clear, evict and put methods now use asynchronous and non-blocking removal of keys when using the Lettuce Redis driver. RedisCache also supports evictIfPresent to remove cache keys immediately which is a blocking method.

Introduce configuration API for RedisCacheWriter.
Also, allow configuration of immediate writes to enforce stronger consistency and visibility of cache writes.

Closes: #3236
Original Pull Request: #3243

Author: mp911de

src/main/java/org/springframework/data/redis/cache/BatchStrategies.java

@@ -100,7 +100,7 @@ public long cleanCache(RedisConnection connection, String name, byte[] pattern)
 	 */
 	static class Scan implements BatchStrategy {
 
-		private final int batchSize;
+		final int batchSize;
 
 		Scan(int batchSize) {
 			this.batchSize = batchSize;