environment-values components for oci-artifacts needs to be revisited.

Summary

With the changes introduced in !6239 (merged) & !6095 (merged), the component environment-values/components/workload-cluster-oci-artifacts is useless as it does the exact same thing as environment-values/components/oci-artifacts. It should be removed and doc updated accordingly.

Additionally, the documentation that sits in environment-values/components/oci-artifacts/README.md to detail the OCI Artifact verification should also be moved into documentation.