auto add reviewrs via Mergify (#1257)

* update mergify nb checks

* lover merge action

* draft auto review

* fix rule

.mergify.yml

@@ -10,7 +10,7 @@ pull_request_rules:
       # no requested chnages from any reviewer
       - "#changes-requested-reviews-by=0"
       # this serves as ALL check has to pass as we have actually 27 tests in total
-      - "#status-success=27"
+      - "#status-success>=27"
       # this is just in case since we rely on GPU tests (note: redundand to the above)
       - status-success=continuous-integration/drone/pr
       # this is patter-like, unofrunatly serves as `any(...)` (note: redundand to the above)
@@ -22,8 +22,12 @@ pull_request_rules:
     actions:
       delete_head_branch: {}
       merge:
-        strict: true  # https://doc.mergify.io/merge-action.html#strict-merge
-        strict_method: rebase
+        # https://doc.mergify.io/merge-action.html#strict-merge
+        # (on head branch) $ git merge --no-ff base
+        # (on head branch) # Wait for CI to go green
+        # (on head branch) # Squash all commits
+        # (on base branch) $ git merge --ff head
+        strict: true
         method: squash
       comment:
         message: Great job! =)
@@ -34,3 +38,12 @@ pull_request_rules:
     actions:
       comment:
         message: This pull request is now in conflict... :(
+
+  - name: add core reviewer
+    conditions:
+      # number of review approvals
+      - "#approved-reviews-by<3"
+    actions:
+      request_reviews:
+        teams:
+          - core-contributors