Add Storybook Implementation MiniToc Component

[martyanovandrey]

We need to add a Storybook entry for the MiniToc component.
https://github.com/diplodoc-platform/components/tree/master/src/components/MiniToc

This will facilitate easier testing, visualization, and documentation of the component for developers and designers.

Tasks:

• Create a new story file for the ToC component in the stories directory.
  https://github.com/diplodoc-platform/components/tree/master/demo/src/Components
• Ensure the Storybook entry demonstrates the component’s basic functionality and key features.
• Implement story controls to allow interactive manipulation of component properties (e.g., different heading levels, styling options).
• Provide clear documentation within Storybook explaining how the component works, including examples of different use cases.

Acceptance Criteria:

• The ToC component appears in Storybook with a variety of examples and variations.
• Interactive controls are available and work as expected.
• Documentation within the Storybook is clear and helpful to users.