Create Dependabot config file (#22)

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

Author: dependabot-preview[bot]

.github/dependabot.yml

@@ -0,0 +1,7 @@
+version: 2
+updates:
+- package-ecosystem: composer
+  directory: "/"
+  schedule:
+    interval: monthly
+  open-pull-requests-limit: 10