Have dependabot run composer update for us

.github/workflows/dependabot.yml

@@ -0,0 +1,18 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://docs.github.com/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
+
+version: 2
+updates:
+  - package-ecosystem: "composer"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+    versioning-strategy: increase-if-necessary
+    allow:
+      - dependency-type: "all"
+    commit-message:
+      prefix: "composer update"
+      include: "scope"