Migrate favicon to svg

[Abdón Rodríguez]

As svg icons are supported in all modern browsers right now, maybe we can update it.

Some references:

• https://medium.com/swlh/are-you-using-svg-favicons-yet-a-guide-for-modern-browsers-836a6aace3df
• https://evilmartians.com/chronicles/how-to-favicon-in-2021-six-files-that-fit-most-needs
• https://catalin.red/svg-favicon-light-dark-theme/

[Abdón Rodríguez]

Would be nice to also addresses light and dark themed:

https://catalin.red/svg-favicon-light-dark-theme/