chore: update dependabot config

[skip ci]

Signed-off-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

.github/dependabot.yml

@@ -2,6 +2,17 @@
 # Make changes to `.github/dependabot.template.yml` and a PR will be automatically created.
 version: 2
 updates:
+  - package-ecosystem: docker
+    open-pull-requests-limit: 20
+    directory: /
+    schedule:
+      interval: weekly
+      day: friday
+      time: '04:00'
+    groups:
+      docker-dependencies:
+        patterns:
+          - '*'
   - package-ecosystem: github-actions
     directory: /
     open-pull-requests-limit: 20