Adapting changes in ERA5Product in command line application

[JuliaKukulies]

A small change has been made for the ERA5Product: When instantiating the product object, the user has now has to choose between ERA5Monthly or ERA5Hourly instead of giving "monthly" or "hourly" as an input argument. This change need to be adapted in the command line tool....maybe we need to come up with a smarter design for the future where such changes to product arguments are directly adapted in the command line tool.