feat(dispatcher): filters.start filter for /start

packages/dispatcher/src/filters.ts

@@ -888,6 +888,15 @@ export namespace filters {
         return check
     }
 
+    /**
+     * Shorthand filter that matches /start commands sent to bot's
+     * private messages.
+     */
+    export const start = and(
+        chat('private'),
+        command('start')
+    )
+
     /**
      * Create a filter for {@link ChatMemberUpdate} by update type
      *