Revert "ci: remove dependabot as we use renovate now (#1597)" (#1615)

This reverts commit 729a4ad.

Author: mshima

.github/dependabot.yml

@@ -0,0 +1,23 @@
+version: 2
+updates:
+  - package-ecosystem: 'npm'
+    directory: '/'
+    schedule:
+      interval: daily
+    open-pull-requests-limit: 5
+    ignore:
+      - dependency-name: '@types/node'
+        versions: ['>=17']
+      - dependency-name: '*'
+        update-types: ['version-update:semver-minor', 'version-update:semver-patch']
+    groups:
+      vitest:
+        patterns:
+          - '@vitest/*'
+          - 'vitest'
+
+  - package-ecosystem: 'github-actions'
+    directory: '/'
+    schedule:
+      interval: 'weekly'
+    open-pull-requests-limit: 5