Add support for placing all Kanban data under specific level-1 header

[DraggonFantasy]

Related issues:

• [Feature]: give the opportunity to add your own information to the note that is not related to tasks #1042
• (somewhat related) Feature Request: Embed kanban board in a page #4

Problem

Sometimes, it’s more convenient to have a Kanban board alongside regular markdown content within the same file. For example, I often have task notes that include subtasks I’d like to track using Kanban, while keeping the task description in the same place. However, with the current implementation, I’m forced to create a separate Kanban note for each case. This results in having two notes for a single task instead of consolidating everything into one note, which feels redundant and less organized.

Solution

This PR introduces the concept of a "Kanban Data Heading". It's a H1 heading that groups all Kanban data under itself. When defined for a Kanban note - the plugin updates only the section of the note, which corresponds to this header. It's inspired by Obsidian Excalidraw's "Back-of-the-card" feature

This setting is not set by default. The default behavior of the plugin is unchanged, the PR only adds this feature as an option. If user wants to enable it for a Kanban note, they can set the Kanban Data Heading in the settings of the board. Also user can "convert" their regular markdown notes to Kanban Note by executing a command "Convert markdown note to Kanban", it automatically adds a new header to the note where the kanban data is placed

Please see the video below for demonstration of the feature:

demo_kanban_1_basic.mp4

Also, this allows the user to combine markdown, kanban and excalidraw all in the same note as demonstrated in the next videos:

demo_kanban_2_excalidraw.mp4

demo_kanban_2_excalidraw2.mp4

NOTE: While I’ve tested various use cases thoroughly, there is still a possibility that this feature could inadvertently affect your data. I strongly recommend creating a backup of your notes before using this feature, especially when enabling it for the first time.