chore: add mergify config (#844)

Author: fgreinacher

.github/mergify.yml

@@ -0,0 +1,13 @@
+pull_request_rules:
+  - name: Automatic merge on approval
+    conditions:
+      - "#approved-reviews-by>=1"
+    actions:
+      merge:
+        method: squash
+  - name: Automatic merge for Renovate pull requests
+    conditions:
+      - author=renovate[bot]
+    actions:
+      merge:
+        method: squash