YAML embedded policy linting

[anderseknert]

Gatekeeper Rego is embedded in custom resource definitions, i.e. YAML files. While there are tools to allow authoring "normal" .rego files and then have them inserted in CRDs, I suppose there are enough people hacking on Rego inside of YAML that it could be useful to be able to lint Rego found in CRDs. Some things — like accurately reporting location – could be tricky, I suppose.