fix: einoagentcli run failed with eino:doc:vector_index: no such index

[cfc4n]

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修复： 首次运行einoagentcli时，报错： eino:doc:vector_index: no such index

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en: When starting the Agent directly, the Redis vector database is allowed to be empty, but the index name must exist. Therefore, when starting the Agent, you need to first determine whether the index exists and perform related initialization actions.
zh(optional): 直接启动Agent时，允许Redis的向量数据库内为空，但索引名字必需存在，所以，需要在Agent启动时，先判断是否存在索引，以及做相关初始化动作。

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[meguminnnnnnnnn]

Hi，运行这个demo有两个启动路径，1. 使用我们提供的eino assistant redis镜像 或者 2. 执行knowledgeindexing初始化redis

这里的首要考虑在于让试用者学习到redis retriever的原理，而不是提供一个很健壮的程序。 因此我觉得隐式初始化redis不是很好的选择。