[BUG] Multiple issues when using a external MILVUS DB

[micuentadecasa]

Description

When using a external Milvus DB the behaviour of Kotaemon is not the same as when using Milvus Lite.

1. The new collection created in Milvus is called index_1 (the default in milvus base), instead of using the one in .env
2. it fails to insert items in the new collection given that the metadata size exceeds the 65535 limit of Milvus

Reproduction steps

1. configure an external db (currently hardcoded)
2. upload a document
3. error

Screenshots

![DESCRIPTION](LINK.png)

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