[milo] Fetch perf/perfbot sheriffs from rotation proxy.

Bug: 1145769,1145768,1071344
Change-Id: I5005d7db18d8fd7393e301da6854a7269d3b9727
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2560524
Auto-Submit: Joey Scarr <jsca@chromium.org>
Commit-Queue: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Cr-Commit-Position: refs/heads/master@{#831901}

infra/config/console-header.star

@@ -96,11 +96,11 @@ HEADER = _header(
         ),
         _oncall(
             name = "Perf",
-            url = "https://rota-ng.appspot.com/legacy/sheriff_perf.json",
+            url = "https://chrome-ops-rotation-proxy.appspot.com/current/grotation:chromium-perf-regression-sheriff",
         ),
         _oncall(
             name = "Perfbot",
-            url = "https://rota-ng.appspot.com/legacy/sheriff_perfbot.json",
+            url = "https://chrome-ops-rotation-proxy.appspot.com/current/grotation:chromium-perf-bot-sheriff",
         ),
         _oncall(
             name = "Trooper",