Clarify pooling is implicitly enabled in Sentinel mode

See gh-27891

Author: weixsun

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/data/redis/RedisProperties.java

@@ -235,7 +235,8 @@ public static class Pool {
 
 		/**
 		 * Whether to enable the pool. Enabled automatically if "commons-pool2" is
-		 * available.
+		 * available.This setting only applies to Jedis when using non-sentinel mode and
+		 * that pooling is implicitly enabled in sentinel mode.
 		 */
 		private Boolean enabled;