Translation for RSS feeds

[Nutomic]

RSS feeds are currently still hardcoded to English, for example:

lemmy/crates/routes/src/feeds.rs

Line 153 in 5204745

title: format!("{} - {}", site_view.site.name, listing_type),

lemmy/crates/routes/src/feeds.rs

Line 460 in 5204745

title: Some(format!("Reply from {creator_name}")),

These should all be translated in the same way as emails:

• Add the text to https://github.com/LemmyNet/lemmy-translations/blob/main/email/en.json
• Make pull request with translation, and use that branch in Lemmy submodule crates/utils/translations/email/
• Use the translated strings with get_interface_language()