Bump Auto Deploy image to v0.12.1

Two new backwards compatible features:

- Allow replicas to be set to zero
- Add option to install and use postgres chart 8.2.1

Add docs on how to use the postgres chart 8.2.1 to be able to deploy to
a Kubernetes 1.16+ cluster.

changelogs/unreleased/auto-deploy-image-v0-12-0.yml

+---
+title: Bump Auto Deploy image to v0.12.1
+merge_request: 26336
+author:
+type: changed

doc/topics/autodevops/index.md

@@ -639,7 +639,8 @@ as it will be attempting to fetch the image using
 
 #### Kubernetes 1.16+
 
-> [Introduced](https://gitlab.com/gitlab-org/charts/auto-deploy-app/-/merge_requests/51) in GitLab 12.8.
+> - [Introduced](https://gitlab.com/gitlab-org/charts/auto-deploy-app/-/merge_requests/51) in GitLab 12.8.
+> - Support for deploying a PostgreSQL version that supports Kubernetes 1.16+ was [introduced](https://gitlab.com/gitlab-org/cluster-integration/auto-deploy-image/-/merge_requests/49) in GitLab 12.9.
 
 CAUTION: **Deprecation**
 The default value of `extensions/v1beta1` for the `deploymentApiVersion` setting is
@@ -657,9 +658,13 @@ To use Auto Deploy on a Kubernetes 1.16+ cluster, you must:
    deploymentApiVersion: apps/v1
    ```
 
-1. Set the `POSTGRES_ENABLED` variable to `false`. This will disable Auto Deploy's deployment of PostgreSQL.
-Support for enabling Auto Deploy's deployment of PostgreSQL in a Kubernetes 1.16+ cluster
-is [planned](https://gitlab.com/gitlab-org/charts/auto-deploy-app/issues/28).
+1. Set the:
+
+   - `AUTO_DEVOPS_POSTGRES_CHANNEL` variable to `2`.
+   - `POSTGRES_VERSION` variable to `9.6.16` or higher.
+
+   This will opt-in to using a version of the PostgreSQL chart that supports Kubernetes
+   1.16 and higher.
 
 #### Migrations
 

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

 .auto-deploy:
-  image: "registry.gitlab.com/gitlab-org/cluster-integration/auto-deploy-image:v0.10.0"
+  image: "registry.gitlab.com/gitlab-org/cluster-integration/auto-deploy-image:v0.12.1"
 
 review:
   extends: .auto-deploy