housekeeping: Add dependabot config file

.github/dependabot.yml

@@ -0,0 +1,13 @@
+version: 2
+updates:
+- package-ecosystem: nuget
+  directory: "/src"
+  schedule:
+    interval: monthly
+    time: "00:00"
+  open-pull-requests-limit: 10
+- package-ecosystem: "github-actions"
+  directory: "/"
+  schedule:
+    # Check for updates to GitHub Actions every weekday
+    interval: "monthly"