Add Dependabot GitHub workflow

Signed-off-by: Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>

.github/dependabot.yml

@@ -0,0 +1,19 @@
+name: Dependabot
+
+version: 2
+updates:
+  - package-ecosystem: "composer"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    assignees:
+      - "sebastian-meyer"
+    labels: [ ]
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    assignees:
+      - "sebastian-meyer"
+    labels: [ ]