Add an example of CI/CD - one that builds Argo Workflows, using Argo Workflows

Users want a more detailed example of doing CI and CD. We should have one that builds Argo Workflows (so it is Argo all the way down):

CI:

* Use webhook to start build (i.e. `WorkflowEventBinding`).
* Build the CLI.
* Build images using Buildkit (see [template](https://github.com/argoproj/argo-workflows/blob/master/examples/buildkit-template.yaml)).
* Run test and collect test report.
* Run coverage and collect report.
* Deploy to a cluster.
* Run basic E2E tests and collect report.

CD:

* Tag and push tag.
* Update deployment manifests using `kustomize edit set image`.
* Commit deployment manifests.
* Start Argo CD sync step (should this use a plugin?).

Pipline:

* Combine CI and CD jobs with an approval step.

Start by reading examples/buildkit-template.yaml, which is the only existing example named in the issue, and review how the requested WorkflowEventBinding and Argo-based steps fit together. Done means a documented example covers the listed CI, CD, combined pipeline, reports, deployment, sync, and approval steps; the issue leaves the plugin choice unresolved.

Written by the indexing model from the issue text.