Create Dependabot config file (#243)

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

.github/dependabot.yml

@@ -0,0 +1,12 @@
+version: 2
+updates:
+- package-ecosystem: cargo
+  directory: "/"
+  schedule:
+    interval: weekly
+  open-pull-requests-limit: 99
+- package-ecosystem: gitsubmodule
+  directory: "/"
+  schedule:
+    interval: weekly
+  open-pull-requests-limit: 99