CEL for function inputs

[johnbelamaric]

[johnbelamaric]

kptdev/kpt#3964 is the kpt issue. We should implement that upstream, ideally.

[johnbelamaric]

kptdev/krm-functions-sdk#678 is a building block

[johnbelamaric]

We should take into consideration as we move forward with the plan laid out in #450 (it is mentioned there).

There is no deliverable for this for R2.