Use dependabot to keep dependencies up to date (#1664)

Author: rjmholt

.github/dependabot.yml

@@ -0,0 +1,20 @@
+version: 2
+registries:
+  powershell-gallery:
+    type: nuget-feed
+    url: https://www.powershellgallery.com/api/v2/
+  nuget-org:
+    type: nuget-feed
+    url: https://api.nuget.org/v3/index.json
+
+updates:
+- package-ecosystem: nuget
+  directory: "/"
+  schedule:
+    interval: daily
+    time: "13:00"
+    timezone: America/LosAngeles
+  open-pull-requests-limit: 10
+  registries:
+  - powershell-gallery
+  - nuget-org