add config for commit signing

Author: skarimo

repository.datadog.yaml

@@ -4,3 +4,11 @@ kind: stale-branches
 max_age: 2920h # 4 months
 excludes:
   - gh-pages
+---
+schema-version: v1
+kind: mergegate
+rules:
+  - require: commit-signatures
+    excluded_emails:
+      - "41898282+github-actions[bot]@users.noreply.github.com" # github-actions[bot]
+      - "[email protected]" # ci.datadog-api-spec bot we use to commit changes