github: sync mergify rules that handle aged PRs

In samba-operator we updated the mergify rules to label PRs that are
"old", applying a "priority-review" label to the PR.  See the
samba-operator commit d2e55778920d3ab0bfd9c7f820fe5b1f2b9de4e4 for full
details.

Signed-off-by: John Mulligan <[email protected]>

Author: phlogistonjohn

.github/mergify.yml

@@ -48,10 +48,12 @@ pull_request_rules:
       - or:
         # Any contributor's PR can be automerged with 2 (or more) reviews.
         - "#approved-reviews-by>=2"
-        # A maintainer's contribution only needs 1 review BUT we give a grace
-        # period over just two weeks for a 2nd reviewer to hopefully appear.
+        # A maintainer's contribution that has already aged long enough to
+        # earn the "priority-review" label can be merged immediately.
+        # The label can also be applied manually in case of an important
+        # bugfix, etc.
         - and:
-          - "updated-at<15 days ago"
+          - "label=priority-review"
           - "author=@maintainers"
           - "#approved-reviews-by>=1"
     actions:
@@ -65,3 +67,17 @@ pull_request_rules:
       comment:
         message: "This pull request now has conflicts with the target branch.
         Please resolve these conflicts and force push the updated branch."
+  # Label PRs that have been sitting there unchanged, aging like a fine wine
+  #
+  # NOTE: the updated-at "counter" resets every time the PR is changed so
+  # reacting to a reviewer's feedback and fixing a typo (for example) will
+  # reset the counter. Thus we now apply a label once we hit the 15 day window
+  # so that we know that PR had, at some time, sat unchanged for that long.
+  - name: Label aged PRs
+    conditions:
+      - "updated-at<15 days ago"
+      - "-draft"
+    actions:
+      label:
+        add:
+          - "priority-review"