ci: create a 'complete-pr' task to block PRs from landing

Author: ahal

taskcluster/kinds/complete/kind.yml

@@ -0,0 +1,23 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+---
+loader: taskgraph.loader.transform:loader
+
+transforms:
+  - taskgraph.transforms.from_deps
+  - taskgraph.transforms.task
+
+kind-dependencies:
+  - check
+  - test
+
+tasks:
+  pr:
+    description: Ensures required PR tasks have completed
+    run-on-tasks-for: ["github-pull-request"]
+    worker-type: succeed
+    from-deps:
+      group-by: all
+      set-name: false
+      unique-kinds: false