创建知识库文件和修改知识库文件接口不支持设置按层级分类

目前/knowledge/document/create接口和/knowledge/document/update 均不支持chunk_type为2的类型，导致需要使用该分段策略时，只能手动选择。希望能够尽快支持该参数

Start by locating the handlers and request validation for /knowledge/document/create and /knowledge/document/update, then trace how chunk_type is processed. Verify the existing behavior for chunk_type 2 and add or update the relevant API tests. Done means both interfaces accept chunk_type 2 so hierarchical classification can be selected through the API.

Written by the indexing model from the issue text.