The Git and OCI clients have their own methods that run before actually performing a fetch operation (named cloneRepo and createRepository respectively). For consistency between clients, and similar to the PreparePush method for the Push operation, we should implement a PrepareFetch method with the following signature:

PrepareFetch(url *netutil.URL, auth *netutil.BasicAuth, opts *options.Options) error

Consequently, the top level Fetch function must be updated to call PrepareFetch before it calls the specialized client's Fetch method.