Add Dependabot configuration

With this set up, you'll automatically get PRs from [Dependabot](https://github.com/dependabot) for most of your dependencies - base images for your Dockerfiles, Github Actions in your workflows, and npm packages for the frontend and backend.

.github/dependabot.yaml

@@ -0,0 +1,18 @@
+version: 2
+updates:
+  - package-ecosystem: "docker"
+    directory: "/"
+    schedule:
+      interval: "daily"
+  - package-ecosystem: "github-actions"
+    directory: "./github/workflows"
+    schedule:
+      interval: "daily"
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "daily"
+  - package-ecosystem: "npm"
+    directory: "/backend/"
+    schedule:
+      interval: "daily"