Add a logo to the Olivero subtheme

Problem/Motivation

Easy Email Theme is being updated to use the theme logo for the email template by default, rather than requiring a separate one to be configured: 📌 Email logo is hard to know where to set Active .

This works much better, but our theme currently relies on the logo from core Olivero, so we need to add it to our subtheme for this feature to work as expected.