Is your feature request related to a problem? Please describe.

Some time ago you implemented a feature I had requested a while ago (my requests here), that is, the --base-class-map flag and also the --enum-field-as-literal-map. This is really nice because I don't have to create hacks in the templates anymore.

However, in my case, I have several classes that I need to map. So, I created a bash script with a string that represents the JSON string. However, maybe we could also have the possibility to specify these mappings in a JSON file and just allow us to pass the file, like we already can do for --extra-template-data. Maybe it's already possible to do this, but I didn't check carefully, so I'm opening it.

Describe the solution you'd like

So, the solution is just to allow us to specify the JSON file instead of forcing us to specify the inline JSON string for these 2 new parameters.

Describe alternatives you've considered

Right now, I need to define this JSON string in a bash. It's OK, but maybe it cleaner to have just the JSON with it?

Additional context
Add any other context or screenshots about the feature request here.