Change ValueError into RepositoryNotSupportedError

[J535D165]

This PR introduces a new error for not supported repositories. This change might be breaking when you catch the ValueError for "Data protocol not found".

import datahugger

try:
    datahugger.get("my_doi", "data")
except datahugger.RepositoryNotSupportedError:
    print("Datahugger doesn't support this resource")
except Exception:
   print("Unexpected error")