add mergify conf

.mergify.yml

@@ -0,0 +1,15 @@
+pull_request_rules:
+  - name: Automatic merge on approval
+    conditions:
+      - "#approved-reviews-by>=1"
+    actions:
+      merge:
+        method: merge
+  - name: automatic merge for Dependabot pull requests
+    conditions:
+      - author~=^dependabot(|-preview)\[bot\]$
+      - check-success=CI - test and coverage / test (pull_request)
+      - title~=^Bump [^\s]+ from ([\d]+)\..+ to \1\.
+    actions:
+      merge:
+        method: merge