Re-enable Dependabot

.github/dependabot.yml

@@ -0,0 +1,28 @@
+version: 2
+updates:
+  - package-ecosystem: bundler
+    directory: /
+    schedule:
+      interval: daily
+
+  - package-ecosystem: npm
+    directory: /
+    schedule:
+      interval: daily
+
+  # Ruby needs to be upgraded manually in multiple places, so cannot
+  # be upgraded by Dependabot. That effectively makes the below
+  # config redundant, as ruby is the only updatable thing in the
+  # Dockerfile, although this may change in the future. We hope this
+  # config will save a dev from trying to upgrade ruby via Dependabot.
+  - package-ecosystem: docker
+    ignore:
+      - dependency-name: ruby
+    directory: /
+    schedule:
+      interval: weekly
+
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: daily