GitLab

* Fixing repo_id regex validation error on windows platforms

* Validating correct URL with prefix is provided

If we are loading a URL then we don't need to use os.path.join and array slicing to split out a repo_id and file path from an absolute filepath. 

Checking if the URL prefix is valid first before doing any URL splitting otherwise we raise a ValueError since neither a valid filepath or URL was provided.

* Style fixes

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Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>