`cloudName` required unnecessarily

In https://github.com/cloudinary/js-url-gen/blob/e1b97191fff165b6ecb353acb2477cc25a062667/src/assets/CloudinaryFile.ts#L182-L193 a `cloudName` setting is explicitly required. However, in https://github.com/cloudinary/js-url-gen/blob/e1b97191fff165b6ecb353acb2477cc25a062667/src/internal/url/cloudinaryURL.ts#L20-L51 the `cloudName` isn't actually even utilized if using a `secureDistribution` and `privateCDN`.

The check for `cloudName` should be moved into `getUrlPrefix` and we should only throw when omitting the cloud name for branches where it's actually utilized.