Added a favicon, merry christmas!!!

[DeaSTL]

Description

Added favicon.svg and link in base

Corresponding issue:

Testing

Ensured the favicon appears on the browser tab with zola serve

Checklist

• [x] I have read the contribution guidelines
• [x] I have targeted this PR against the correct branch (master for website changes, dev for source changes)
• [x] This is either a bugfix, a documentation update, or a new feature that has been explicitly approved via an issue
• [x] I ran the test suite locally (npm run test) and verified that it succeeded