Enable output capture for subsequent steps

I want to be able to print the output as a comment on the triggering pull request for my workflow with something like `steps.kubeval.outputs.stdout`, which doesn't appear possible as yet

Start by reviewing the kubeval-action repository's action entry point and how it currently handles command output. Confirm how a workflow step can expose stdout for later steps, then verify that a subsequent step can reference the output as steps.kubeval.outputs.stdout and use it in a pull-request comment.

Written by the indexing model from the issue text.