Adds the status upgrade check for the JSON to YAML migration
effort and updates the documentation where it seems appropriate
to move from "policy.json" to "policy.yaml"
Mostly shamelessly copied from https://review.opendev.org/#/c/748059/
however is in-line with ironic's configuration and patching methods.
Related Blueprint: policy-json-to-yaml
Change-Id: I1d5b3892451579ebfd4d75a0f7185e0ef3c984c8
2404d486ac