Add favicon to kedro-viz documentation

[Huongg]

Description

Fixes #1724 , as a part of the ticket is to add the favicon to our documentation. Ideally we should do it directly in kedro-sphinx-theme.

However @astrojuanlu pointed out that there's some issue with Sphinx theme don't normally have their own conf.py (issue here), therefore the fix for now will be directly inside kedro-viz doc, and the same for kedro datasets

The favicon is now shown through the doc build https://kedro--1959.org.readthedocs.build/projects/kedro-viz/en/1959/

Checklist

• [ ] Read the contributing guidelines
• [ ] Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• [ ] Updated the documentation to reflect the code changes
• [x] Added new entries to the RELEASE.md file
• [ ] Added tests to cover my changes