Switch default search engine to DuckDuckGo

Upstream Tor Browser has done that, since disconnect.me keeps on redirecting to duckduckgo and users are annoyed/scared by that. We should switch our localization extension to use duckduckgo too.

Feature Branch: feature/11913-ddg-as-default-in-tor-browser

Related issues

Has duplicate #11845 (closed)

Original created by @bertagaz on 11913 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information