chore: standardize dependabot config

Author: fey

.github/dependabot.yml

@@ -0,0 +1,21 @@
+version: 2
+updates:
+  - package-ecosystem: "terraform"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    open-pull-requests-limit: 1
+    groups:
+      all-terraform-dependencies:
+        patterns:
+          - "*"
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    open-pull-requests-limit: 1
+    groups:
+      all-github-actions-dependencies:
+        patterns:
+          - "*"