feat: added support for exporting DocItem to an image when page image is available

[sh-gupta]

Updated the minimum docling-core version to 2.4.0 so that DocItem now supports the get_image function. One can now get the image corresponding to any DocItem as long as PdfPipelineOptions.generate_page_images = True.

Deprecated the PdfPipelineOptions.generate_table_image as this option is equivalent to setting PdfPipelineOptions.generate_page_images = True and then using TableItem.get_image.

Issue resolved by this Pull Request: Resolves #299

Checklist:

• [x] Documentation has been updated, if necessary.
• [x] Examples have been added, if necessary.
• [x] Tests have been added, if necessary.

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