Add AVIF media type registrations

The new media type is submitted to IANA but has not been formally
published by IANA yet. Both Firefox and Chromium are already using
the mime type for AVIF images.

Citation: https://aomediacodec.github.io/av1-avif/#mime-registration

src/mime_types.rs

@@ -102,6 +102,7 @@ pub static MIME_TYPES: &[(&str, &[&str])] = &[
     ("atx", &["application/vnd.antix.game-component"]),
     ("au", &["audio/basic"]),
     ("avi", &["video/x-msvideo"]),
+    ("avif", &["image/avif"]),
     ("aw", &["application/applixware"]),
     ("axa", &["audio/annodex"]),
     ("axs", &["application/olescript"]),