API-driven asynchronous credential verification

[skateman]

The DDF forms require the verification to be asynchronous and API-driven, ideally without having anything stored in the database. I was able to implement the validation for the default endpoint by using raw_connect. However, the non-primary (prometheus, hawkular, kubevirt) endpoints are a little bit complicated as all the verification methods are in a record's context and as far as I see, I'd need to create some DB records to be able to validate these endpoints.

I could possibly reimplement the wheel and recreate the validation without bindings to records, but this is my first time doing anything in this repo and I don't want to introduce technical debt. So I'm asking for some help to have context-free parameter-only methods for validating hawkular, prometheus and kubevirt.

Parent issue: ManageIQ/manageiq#18818