feat: add the concept of tags

Tags are attached to all magnet links provided by a given source, and
passed to actions. This allows for e.g. better categorization in
Bitmagnet.

src/main.rs

@@ -28,6 +28,7 @@ pub struct PostInfo {
     pub subreddit: String,
     pub timestamp: DateTime<Utc>,
     pub imdb_id: Option<String>,
+    pub tags: Vec<String>,
 }
 
 #[tokio::main]