add mergify

Mergify automatically merges pull requests when they're ready so you
don't have to. You set the rules, it does the rest.

Signed-off-by: Sébastien Han <seb@redhat.com>

.mergify.yml

@@ -0,0 +1,10 @@
+rules:
+  default:
+    protection:
+      required_status_checks:
+        strict: true
+        contexts:
+          - DCO
+          - "Testing: ceph-ansible PR Pipeline"
+      required_pull_request_reviews:
+        required_approving_review_count: 1