[Infrastructure] Configure dependabot to update GitHub actions (AliceO2Group#10660)

Author: vkucera

.github/dependabot.yml

@@ -0,0 +1,10 @@
+---
+# Dependabot configuration
+# Reference: https://docs.github.com/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions" # See documentation for possible values
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "weekly"