Allow read_config_file() and read_config() to take URLs as inputs and add SubTreeFileSystem class method to read_config_file()

[annakrystalli]

See https://github.com/hubverse-org/hubValidations/pull/196 fo for context

[annakrystalli]

Actually this is a bit more involved given we currently support both s3 bucket paths and local paths. I was trying to avoid having to class specific methods of read_config_file() as the idea was that it would primarily be called via read_config() which does have class methods and performs a lot of validation also. However, I'm going to go ahead and add class specific methods to read_config_file(). In the default method, I'll also allow it to read a config file from a url (e.g. GitHub) which would allow modelers not working within a hub to have an up to date version of a config file.