Update auto-build-image with CNB support

changelogs/unreleased/update-auto-build-image-with-cnb-support.yml

+---
+title: Add initial support for Cloud Native Buildpacks in Auto DevOps builds
+merge_request: 28165
+author:
+type: added

doc/topics/autodevops/index.md

@@ -404,6 +404,33 @@ If Auto Build fails despite the project meeting the buildpack requirements, set
 a project variable `TRACE=true` to enable verbose logging, which may help to
 troubleshoot.
 
+#### Auto Build using Cloud Native Buildpacks (beta)
+
+> Introduced in [GitLab 12.10](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/28165).
+
+Auto Build supports building your application using [Cloud Native Buildpacks](https://buildpacks.io)
+through the [`pack` command](https://github.com/buildpacks/pack). To use Cloud Native Buildpacks,
+set the CI variable `AUTO_DEVOPS_BUILD_IMAGE_CNB_ENABLED` to a non-empty value.
+
+Cloud Native Buildpacks (CNBs) are an evolution of Heroku buildpacks, and
+will eventually supersede Herokuish-based builds within Auto DevOps. For more
+information, see [this issue](https://gitlab.com/gitlab-org/gitlab/-/issues/212692).
+
+Builds using Cloud Native Buildpacks support the same options as builds using
+Heroku buildpacks, with the following caveats:
+
+- The buildpack must be a Cloud Native Buildpack. A Heroku buildpack can be
+  converted to a Cloud Native Buildpack using Heroku's
+  [`cnb-shim`](https://github.com/heroku/cnb-shim).
+- `BUILDPACK_URL` must be in a form
+  [supported by `pack`](https://buildpacks.io/docs/app-developer-guide/specific-buildpacks/).
+- The `/bin/herokuish` command is not present in the resulting image, and prefixing
+  commands with `/bin/herokuish procfile exec` is no longer required (nor possible).
+
+NOTE: **Note**: Auto Test still uses Herokuish, as test suite detection is not
+yet part of the Cloud Native Buildpack specification. For more information, see
+[this issue](https://gitlab.com/gitlab-org/gitlab/-/issues/212689).
+
 ### Auto Test
 
 Auto Test automatically runs the appropriate tests for your application using
@@ -1162,6 +1189,7 @@ applications.
 |-----------------------------------------|------------------------------------|
 | `ADDITIONAL_HOSTS`                      | Fully qualified domain names specified as a comma-separated list that are added to the Ingress hosts. |
 | `<ENVIRONMENT>_ADDITIONAL_HOSTS`        | For a specific environment, the fully qualified domain names specified as a comma-separated list that are added to the Ingress hosts. This takes precedence over `ADDITIONAL_HOSTS`. |
+| `AUTO_DEVOPS_BUILD_IMAGE_CNB_ENABLED`   | When set to a non-empty value and no `Dockerfile` is present, Auto Build builds your application using Cloud Native Buildpacks instead of Herokuish. [More details](#auto-build-using-cloud-native-buildpacks-beta). |
 | `AUTO_DEVOPS_BUILD_IMAGE_EXTRA_ARGS`    | Extra arguments to be passed to the `docker build` command. Note that using quotes will not prevent word splitting. [More details](#passing-arguments-to-docker-build). |
 | `AUTO_DEVOPS_BUILD_IMAGE_FORWARDED_CI_VARIABLES` | A [comma-separated list of CI variable names](#passing-secrets-to-docker-build) to be passed to the `docker build` command as secrets. |
 | `AUTO_DEVOPS_CHART`                     | Helm Chart used to deploy your apps. Defaults to the one [provided by GitLab](https://gitlab.com/gitlab-org/charts/auto-deploy-app). |

lib/gitlab/ci/templates/Jobs/Build.gitlab-ci.yml

 build:
   stage: build
-  image: "registry.gitlab.com/gitlab-org/cluster-integration/auto-build-image/master:stable"
+  image: "registry.gitlab.com/gitlab-org/cluster-integration/auto-build-image:v0.2.0"
   variables:
     DOCKER_TLS_CERTDIR: ""
   services: