Update dependabot.yml

Author: palpalani

.github/dependabot.yml

@@ -5,3 +5,13 @@ updates:
     schedule:
       interval: daily
     open-pull-requests-limit: 10
+  
+  # Maintain dependencies for Composer.
+  - package-ecosystem: composer
+    directory: "/"
+    schedule:
+      interval: monthly
+    labels:
+      - dependencies
+    versioning-strategy: increase-if-necessary
+    rebase-strategy: disabled