ci: add dependabot config (github-actions + cargo)

Author: willemneal

.github/dependabot.yml

@@ -0,0 +1,21 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly
+    groups:
+      actions-minor:
+        update-types:
+          - minor
+          - patch
+
+  - package-ecosystem: "cargo"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    groups:
+      cargo-minor:
+        update-types:
+          - minor
+          - patch