suggestion: change from feathericons to simpleicons

Since feather icons are not going to add more brand icons (see issue below), would it be feasible for this project to switch to another theme provider? E.g., icon theme for Mastodon won't be added which is a large social media site(s).

https://github.com/feathericons/feather/issues/763

Start by locating how Feather Icons are used across the Archie Hugo theme, then review Simple Icons coverage for the requested brand icons such as Mastodon. Done means the replacement provider is integrated without breaking existing icon usage and the requested brands are available.

Written by the indexing model from the issue text.