ci: Enable automated update PRs from dependabot (#880)

.github/dependabot.yml

@@ -0,0 +1,18 @@
+# Please see the documentation for all configuration options:
+# https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
+
+version: 2
+updates:
+  - package-ecosystem: "cargo"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+  # pnpm is handled by the "npm" package ecosystem
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "weekly"