Add Storybook Implementation ToC Component

We need to add a Storybook entry for the Table of Contents (ToC) component.
https://github.com/diplodoc-platform/components/tree/master/src/components/Toc

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.

Start by inspecting the ToC component in src/components/Toc and the existing stories under demo/src/Components. Run the Storybook setup to understand its current patterns, then add the ToC entry with examples, controls, and explanatory documentation. Done means the component appears with varied examples and its controls work as described in the acceptance criteria.

Written by the indexing model from the issue text.