Add Dependabot (#1136)

* add dependabot config

* increase PR limit

.github/dependabot.yml

@@ -0,0 +1,17 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    # default location of `.github/workflows`
+    directory: "/"
+    open-pull-requests-limit: 10
+    schedule:
+      interval: "weekly"
+
+  - package-ecosystem: "nuget"
+    # location of package manifests
+    directory: "/"
+    open-pull-requests-limit: 10
+    schedule:
+      interval: "daily"
+
+# Built with ❤ by [Pipeline Foundation](https://pipeline.foundation)