Add ACM source, sink, vet functions

[frankfarzan]

source: Hydrate ACM repo
vet: Run validations rules
sink: Write configs into ACM repo format

[linde]

main concerns here is that it would be nice to be able to supply gcr.io/kpt-functions/write-yaml parameters to name folders so one could respectively:

• enclose the cluster scoped resources
• serve as the top level directory in which namespace specific sub-directories are contained

with these two parameters, or an equiv more elegant approach (low bar that!) one would be able to take a kpt resource list and have it written into a configuration root for an ACM repo. this could be handy in a CI step that takes unstructured config from off the shelf tool output or operator manifests and keeps them in sync in an otherwise structured gitops layout.

in the ACM case, if we did it right, this would essentially be the "dehydrate" counterpart to the nomos hydrate sub-command.

[frankfarzan]

Agree. I think a good design is to have symmetry between sources and sink, i.e. read-acm-dir/write-acm-dir (Exact name doesn't matter here)

[aw185176]

I am interested in implementing this for our internal usage, but ran into issues because kpt won't allow the path annotation to reference directories. There are quite a few libraries under kyaml and I am not fully up to speed on working with the RNode representation of my document. Assuming that I can write a program which calls Read on the ResourceList passed in via stdin, what would be the easiest path towards writing the individual documents to the file system?

[bgrant0607]

cc @janetkuo

[bgrant0607]

For dehydrate, there's https://github.com/dippynark/kfmt

However, we're primarily recommending the unstructured format.

Nonetheless, vet and hydrate would be useful as functions.