Update to the tutorial section of the documentation and the MKdocs configs

Summary

This branch includes updates to the tutorials section of the NOMAD documentation, along with improvements to styling and functionality to support image sliders and enhanced formatting.

Tutorial Pages

1. Created a new overview page
   → overview.md

2. Removed the "Navigation to NOMAD" page

3. Replaced the content of:

   • upload_publish.md – Uploading and Publishing Data
   • explore.md – Exploring Data

4. Added a new tutorial
   → NOMAD_ELN.md – Using NOMAD as an ELN

Configuration Changes

mkdocs.yml

• Updated the nav section to reflect the new tutorial structure

javascript.js

• Added a script to enable image sliders (horizontal image navigation)

extra.css

• Added styles and classes for image sliders

Writing Guide Updates

• Added instructions for preparing image sliders in documentation
• Introduced three new admonitions used across tutorials:
  • !!! example
  • !!! task
  • !!! info

Closes #2287 (closed)