Add primary key and cursor key support for LLM document creation

```
# TODO: Add primary key and cursor key support:
```

https://github.com/airbytehq/PyAirbyte/blob/73eaa0ee5a04d2e5fac086d8662a52b612584039/airbyte/_util/document_rendering.py#L45

Start at airbyte/_util/document_rendering.py around line 45 and trace how LLM documents are created and consumed. Clarify the expected primary-key and cursor-key inputs and their rendered representation before making the change. Done means document creation supports both kinds of keys without leaving the TODO unresolved.

由索引模型根据 Issue 内容生成。