Refactor Google export process

[ybekdemir]

Google import and export methods are very open to create new bugs, code is not readable and not suitable for PEP8. Also, methods include unnecessary codes and logical mistakes. In order to make google export code more readable and maintainable, we should refactor google export methods and increase test coverage for them.

Methods to be refactor for export process :
def export_to_gsheet_helper(user, spreadsheet_id, silo_id, query, headers):
def export_to_gsheet(request, id):