[skip e2e]Update default consistency level in doc (#15356)

Signed-off-by: Nyanliang567 <yanliang.qiao@zilliz.com>

docs/developer_guides/how-guarantee-ts-works-cn.md

@@ -59,5 +59,5 @@ syncTs1 为例，当下游消费者（比如QueryNodes）看到 syncTs1，那么
 - 客户端一致性：客户端使用上一次写入的时间戳作为 GuaranteeTs，那么每个客户端至少能看到
 自己插入的全部数据。
 
-Milvus 默认提供强一致性，如果用户不传入 GuaranteeTs，那么会将 GuaranteeTs 设为系统
+Milvus 默认提供有界一致性，如果用户不传入 GuaranteeTs，那么会将 GuaranteeTs 设为系统
 当前的最新时间戳。

docs/developer_guides/how-guarantee-ts-works.md

@@ -77,4 +77,4 @@ As shown in the figure below, different GuaranteeTs correspond to four different
 - Read your own write (Session): Set GuaranteeTs to the client last write, in this way, every client will see all their
   own data.
 
-Milvus provides strong consistency by default.
+Milvus provides bounded staleness consistency by default.