[#75691732] Document vcloud-core public methods

> According to semver http://semver.org/ we should document the API
> (lower case should). We should document this by adding Yard
> documentation to public methods. See [#73962736] for an example.
You can use the private keyword which affects how it shows up in the API [example](https://github.com/gds-operations/vcloud-core/blob/7ddf256a74119fcdb6b2e57b3208ed346625fc29/lib/vcloud/core/fog/model_interface.rb#L9)