feat: allow kustomize-build and helm-template promotion steps to break up output into a file per resource

[krancour]

Exactly what the title says.

Kargo Render had this option and I believe our new promotion steps would benefit from having this as well.

Note: If we port this functionality over from Kargo Render, I believe there is an open, but as-yet-unreviewed PR with a bug fix for that bit of code and it ought to be taken into account: akuity/kargo-render#305