feat: WA Business Labels support (#407)

* Get all labels
* Get chats by label
* Get labels assigned to chats

Co-authored-by: Pedro S. Lopez <pslamoros@hotmail.com>
Co-authored-by: Pedro Lopez <pedroslopez@me.com>

src/structures/index.js

@@ -10,5 +10,6 @@ module.exports = {
     MessageMedia: require('./MessageMedia'),
     PrivateChat: require('./PrivateChat'),
     PrivateContact: require('./PrivateContact'),
-    GroupNotification: require('./GroupNotification')
+    GroupNotification: require('./GroupNotification'),
+    Label: require('./Label.js')
 };