Support for cue cmd

[lorenzofelletti]

Idea

Support workflow-like CUE code, equivalent to cue cmd: https://cuelang.org/docs/reference/command/cue-help-cmd/

Motivation And Use cases

• Support for "vendoring" helm charts by adding CUE constraints to validate input values, and optionally unify rendered templates with some additional configuration coming from CUE code (e.g. enforcing certain securityContext values, or add resources, or any other edit to the output templates).

• Allow for pre-steps to supply values to CUE, or run some commands as part of a pipeline-like flow.