Add Dependabot Docker update coverage for container image supply chain (#49528)

* Initial plan

* Plan dependabot docker coverage

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Add weekly Dependabot docker update entries

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
Co-authored-by: Peli de Halleux <pelikhan@users.noreply.github.com>

Author: Copilot

.github/dependabot.yml

@@ -24,3 +24,15 @@ updates:
   directory: /.github/workflows
   schedule:
     interval: weekly
+- package-ecosystem: docker
+  directory: /
+  schedule:
+    interval: weekly
+- package-ecosystem: docker
+  directory: /actions/setup/js
+  schedule:
+    interval: weekly
+- package-ecosystem: docker
+  directory: /.devcontainer
+  schedule:
+    interval: weekly