Allow 'apicurio.codegen.openapi.spec' to optionally point to a YAML file

[theseeker58]

Is it possible to set apicurio.codegen.openapi.spec property with a yaml file?
I tried but nothing happens; no exceptions either.

I tried to convert yaml to json and the generation succedes, but while model classes are successfully generated removing hyphens and underscores, resource class keeps not allowed characters and so compilation fails. I attach openapi downloaded from the Berlin Group (https://www.berlin-group.org/openfinance-downloads)
RTP_SCTv1_0_0__20220303.yaml.zip

[EricWittmann]

I think supporting YAML files is sensible. That shouldn't be a big problem.

As for the failed compilation for the Berlin Group API - that will need some investigation and I'll open a separate GH issue for it.