[blog] how to do push/sign with GitLab CI then verify/pull with Flux

[nagyv]

As discussed in Slack, I'd like to write a blog post on how to use Flux with GitLab and cosign with OCI artifacts.

Proposal

A blog post of

• package and push a minimal k8s app with GitLab pipelines to the GitLab container registry as an OCI artifact
• sign the artifact
• trigger immediate reconciliation
• create a pipeline with automatic deployment to staging and manual deployment for production (the OCI for production is built after a manual action)
• "appendix" on building a custom image with cosign+flux+jq bundled together to be used in the pipeline

[nagyv]

Please, assign this to me :)