Allow Tasks/Pipelines to indicate versions of Tekton Pipelines they work with

[bobcatfish]

Expected Behavior

Before I try to use a Task or a Pipeline, I should know if it is compatible with my installation of Tekton Pipelines just by looking at it.

Actual Behavior

Right now the only indication is the apiVersion, currently with possible values of v1alpha1 and v1beta1. But additive changes can be made between releases.

Steps to Reproduce the Problem

For example v0.12.0 introduces Pipeline level results, which are not present in v0.11.0, although they are both v1beta1. This means that defining a Pipeline which declares results and trying to use it against a v0.11.0 installation will fail. (We could work around this by allowing versions to ignore fields they don't recognize, but even in that case the expected behavior would not be present.)

Additional Info

• This is different from Feature: Versioning on Tasks/Pipelines #1839 which is about versioning Tasks + Pipelines themselves (e.g. adding/removing params)
• This is highly relevant to discussions beginning around increasing the level of testing for https://github.com/tektoncd/catalog (we need to know what versions of Tekton Pipelines to test against)

[bobcatfish]

Proposal for using annotations in this design doc.

[bobcatfish]

We've started using the tekton.dev/minVersion annotation in tektoncd/catalog#389.

Seems okay to close this issue now then :D We could still have the controller fail if the minVersion is > than it's own version but that's another story.