feat: add mastodon_screen_name to config struct

src/config.rs

@@ -22,6 +22,7 @@ pub struct TwitterConfig {
 #[derive(Debug, Deserialize)]
 pub struct MastodonConfig {
     pub twitter_screen_name: String,
+    pub mastodon_screen_name: Option<String>,
     pub twitter_page_size: Option<i32>,
     pub base: String,
     pub client_id: String,