equipment_from_json uses filename

[RenatoParker]

In the json_io.py, the function equipment_from_json at line 396 is using filename as an argument.

This filename is then passed to the method from_json in the class Amp, defined in the same file at line 193.

This filepath is used to load the file default_edfa_config.json.

This raises two main issues:

1. While using the function equipment_from_json, a filename must be specified. This does not allow the function to parse JSON data that doesn't come from files.
2. If a user is using gnpy, the file default_edfa_config.json must be provided.

I suggest defining the default_edfa_config information within the code.