add sep to kv_to_csv

[DGarbs51]

adding an optional sep argument to the export_kv_to_csv function

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[Chuukwudi]

This is indeed a useful feature! I recently submitted a PR that was approved, but it focused on the document level rather than the page level.

May I suggest to @Belval: While we currently have separate functions to export to formats like XLSX and CSV, it might be beneficial to introduce a feature that allows direct export to pandas, similar to the to_pandas() methods available in the table class. This would leverage pandas' built-in export methods, such as to_html, to_csv, to_excel, to_markdown, and others, simplifying the workflow and reducing redundancy.

I have already created a PR to enable this functionality, but implementing it at the page level as well would further enhance usability.

The key_values feature is incredibly useful, and adding the capability to export directly to pandas would make it even more powerful.