Add support for newest ForumChannel changes

This adds the following:

- Forum tag support
- Default reaction support
- Default slowmode for newly created threads

discord/http.py

@@ -1143,7 +1143,12 @@ class HTTPClient:
             'invitable',
             'default_auto_archive_duration',
             'flags',
+            'default_thread_rate_limit_per_user',
+            'default_reaction_emoji',
+            'available_tags',
+            'applied_tags',
         )
+
         payload = {k: v for k, v in options.items() if k in valid_keys}
         return self.request(r, reason=reason, json=payload)