ci: add dependabot config

Author: phaux

.github/dependabot.yml

@@ -0,0 +1,20 @@
+version: 2
+
+updates:
+  - package-ecosystem: npm
+    directory: /
+    schedule:
+      interval: monthly
+    groups:
+      typescript-eslint:
+        patterns:
+          - "@typescript-eslint/*"
+    ignore:
+      - dependency-name: eslint
+        update-types:
+          - version-update:semver-major
+
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: monthly