Re-work the openapi schema issue in tektoncd/pipeline

See https://github.com/tektoncd/pipeline/issues/1461

We need to fix this (for a lot of reason). Let's start with tektoncd/pipeline and once this is fixed there, apply to all of the other components.

We either need to relay on existing tooling (linked in upstream issue) or adapt and write our own, for our own use case.

• Decide what to add in the schema (we don't need to include all Pod/Container like Volume, … we can link to them)
• Try to see if it would fit into the etcd size limit with v1beta1 and v1
• Write a tool (or adapt a tool) that generates this from code.