Add Dependabot configuration for GitHub Actions updates (#3)

## Description

This pull request introduces a Dependabot configuration file to the
repository. This enables automated checks and updates for GitHub Actions
dependencies on a weekly schedule.

Dependency management:

* Added `.github/dependabot.yml` to configure Dependabot for weekly
updates of GitHub Actions dependencies, including relevant labels for
tracking.

Author: MariusStorhaug

.github/dependabot.yml

@@ -0,0 +1,14 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# 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 # See documentation for possible values
+    directory: / # Location of package manifests
+    labels:
+      - dependencies
+      - github-actions
+    schedule:
+      interval: weekly