Enable PR tracking review assignment

Author: apiraino

triagebot.toml

@@ -854,3 +854,7 @@ project-stable-mir = [
 "/src/tools/tidy" =                                      ["bootstrap"]
 "/src/tools/x" =                                         ["bootstrap"]
 "/src/tools/rustdoc-gui-test" =                          ["bootstrap", "@onur-ozkan"]
+
+# Enable tracking of PR review assignment
+# Documentation at: https://forge.rust-lang.org/triagebot/pr-assignment-tracking.html
+[pr-tracking]