[DOC] add swagger live-docs for OFREP

[toddbaert]

Change in the documentation

It would be great if we could serve a live swagger doc for OFREP on the OFREP appendix page (or host it somewhere else on the site and link to it from there). Embedding it directly into the page may be possible, but may require changes to the spec page (this page is pulled into openfeature.dev as a git submodule). Perhaps it could be hosted on openfeature.dev, but rendered in appendix 3 in an iframe?

OFREP OpenAPI spec is available here: https://github.com/open-feature/protocol/blob/main/service/openapi.yaml