Enable the @rustbot ready/author/blocked shortcuts

Given that they can set pretty much all the other flags (including e.g.
nominating an issue) these are part of the regular issue/ACP workflow
and thus seem sensible to add.

Author: tomassedovic

triagebot.toml

@@ -18,6 +18,7 @@ allow-unauthenticated = [
     "perf-*",
     "AsyncAwait-OnDeck",
     "initial-comment-period",
+    "waiting-on-author",
 ]
 
 # [major-change]