Requesting improvements to CustomTypeMappings

[stealthAngel]

at the moment to change a type with typegen we can update our tgconfig.json like this:

"customTypeMappings": { "Microsoft.AspNetCore.Http.IFormFile": "File" }

it would be more readable if we changed this to:

  "typeMappings": [
    {
      "sourceType": "Microsoft.AspNetCore.Http.IFormFile",
      "targetType": "File"
    }
  ]

with this approach we can later add more settings if needed.