Add dependabot

Author: discordier

.github/dependabot.yaml

@@ -0,0 +1,21 @@
+version: 2
+
+updates:
+  - commit-message:
+      include: "scope"
+      prefix: "composer"
+    directory: "/"
+    open-pull-requests-limit: 10
+    package-ecosystem: "composer"
+    schedule:
+      interval: "weekly"
+    versioning-strategy: "increase"
+
+  - commit-message:
+      include: "scope"
+      prefix: "github-actions"
+    directory: "/"
+    open-pull-requests-limit: 10
+    package-ecosystem: "github-actions"
+    schedule:
+      interval: "weekly"