Automatically remove "awaiting response" label on-comment (mozilla#1129)

Also will close tickets that have been "awaiting response" for over 15 days.

.github/workflows/awaiting-response.yml

@@ -0,0 +1,19 @@
+name: awaiting response
+on:
+  issue_comment:
+    types: [created]
+  schedule:
+    - cron: '5 * * * *'
+jobs:
+  noResponse:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: lee-dohm/no-response@v0.5.0
+        with:
+          closeComment: >
+            This issue has been automatically closed because it has been blocked for too 
+            long on a response that wasn't provided. Of course, if the needed response
+            is provided later, re-open this ticket so that we can progress it further. :)
+          responseRequiredLabel: awaiting response
+          responseRequiredColor: d4c5f9
+          token: ${{ github.token }}