Update mkdocs with the TOC fix script

[Telucero]

This PR adds the necessary JS line in the mkdocs file to run the script to resolve the (i-1) TOC issue.

Related to Tanssi docs #332

[Copilot]

Pull Request Overview

This PR adds a JavaScript file reference to the mkdocs configuration to fix a table of contents (TOC) scrolling issue. The change integrates an existing TOC fix script into the documentation build process.

• Adds js/fix-toc-scroll.js to the extra_javascript configuration

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