Get last x events from "Vertex Session Events"

listing Vertex Session Events only support the following attributes:

- parent (str):
- page_size (int): These events are ordered by timestamp in ascending order
- page_token (str):
- filter (str):

as "sessions" has order_by attribute, "session events" need to have it also.

首先定位 Vertex Session Events 列表的入口点，并将其与已经支持 order_by 的 sessions 接口进行比较。检查 page_size、page_token 和按 timestamp 排序的处理方式，然后添加覆盖，表明调用方可以请求最后的事件。issue 中没有指定具体的文件或测试。

由索引模型根据 Issue 内容生成。