Add an option to keep the summary content when converting to markdown in rich mode

[Deminhlo]

Hi Team
Markdown is the soul of Obsidian because it is compatible. Markmind in rich text mode is very nice and useful when drawing mindmaps. However, because it stores data in JSON format, it is not compatible with other Markdown-formatted content such as outlines, tables, or a regular note in Markdown format when published to the web.

Markmind currently allows you to copy all the nodes of a mindmap in rich text mode to Markdown format. However, there is no option to keep the contents of the summary (notes) of the nodes.

This is a big omission. If the development team supports Markdown formatting attached to nodes and allows it to be kept when converting a mind map to Markdown format, it is a great idea.

This will increase the compatibility for the Obsidian ecosystem and still retain the full features of a rich text mind map.