Enable review-requested feature for rustbot

Author: WaffleLapkin

triagebot.toml

@@ -29,6 +29,12 @@ reviewed_label = "S-waiting-on-author"
 # These labels are removed when a "request changes" review is submitted. 
 review_labels = ["S-waiting-on-review"]
 
+[review-requested]
+# Those labels are removed when PR author requests a review from an assignee
+remove_labels = ["S-waiting-on-author"]
+# Those labels are added when PR author requests a review from an assignee
+add_labels = ["S-waiting-on-review"]
+
 [glacier]
 
 [ping.icebreakers-llvm]