Toggle Metadata Visibility

[Deep-Analyzer]

Implemented functionalities:

1. Introduce the 'item-collapse' setting to manage card states: collapsed (hidden metadata, encoded as true), expanded (visible metadata, encoded as false), or undefined (no metadata attached, encoded as null).
2. Add a 'Show/Hide Metadata' button (chevron down or chevron right icon) to each card with metadata, allowing users to control metadata visibility.
3. Add a 'Show/Hide Metadata' button in the board's tab menu to control metadata visibility for the entire board. A new setting under 'Board Header Buttons' allows users to disable this feature (hide the button). Implemented behavior:
   • if no cards have metadata, the button click is ignored;
   • if all cards with metadata are either collapsed or expanded, the button toggles their state (make them all expanded or collapsed);
   • if some cards are collapsed and others expanded, clicking the button will collapse all of them.

Merging this PR will close issue #445 ([Feature] Meta Data Toggle Button to Show or Hide), also listed under the Todo section on the Obsidian Kanban Roadmap.

Example screenshots: