docs: Fix Milvus vector store initialization (#29511)

- [x] **PR title**:


- [x] **PR message**:

- A change in the Milvus API has caused an issue with the local vector
store initialization. Having used an Ollama embedding model, the vector
store initialization results in the following error:

<img width="978" alt="image"
src="https://github.com/user-attachments/assets/d57e495c-1764-4fbe-ab8c-21ee44f1e686"
/>

- This is fixed by setting the index type explicitly:

`vector_store = Milvus(embedding_function=embeddings,
connection_args={"uri": URI}, index_params={"index_type": "FLAT",
"metric_type": "L2"},)`

Other small documentation edits were also made.


- [x] **Add tests and docs**:
  N/A


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from the root of the package(s) you've modified. See contribution
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---------

Co-authored-by: Chester Curme <[email protected]>

Author: markperfect