Add Dependabot configuration

Add configuration for Dependabot to automatically update dependencies,
if possible. Updates are currently managed to GitHub Actions as well as
Cargo.toml based Rust dependencies.

.github/dependabot.yml

@@ -0,0 +1,18 @@
+# Copyright (C) 2024 Daniel Mueller <deso@posteo.net>
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# Please see the documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    rebase-strategy: auto
+    directory: /
+    schedule:
+      interval: daily
+  - package-ecosystem: cargo
+    versioning-strategy: auto
+    directory: /
+    schedule:
+      interval: daily