Generate CI images with oci-build-task

Update CI to generate images using an `oci-build-task` since
the `registry-image` resource cannot perform actual image builds.

See gh-24197

ci/tasks/build-ci-image.yml

@@ -0,0 +1,17 @@
+---
+platform: linux
+image_resource:
+  type: registry-image
+  source:
+    repository: vito/oci-build-task
+inputs:
+- name: ci-images-git-repo
+outputs:
+- name: ((ci-image-name))
+caches:
+- path: ci-image-cache
+params:
+  CONTEXT: ci-images-git-repo/ci/images
+  DOCKERFILE: ((ci-image-name))/Dockerfile
+run:
+  path: build