Dynamically generate config for a build variant from a json file

1. Create a configuration json file which contains the keys for a particular variant (check out the example)
2. Execute flutter packages pub run build_runner build --define "dynamic_config_generator|config_builder=variant=$variant"
3. This will create build_config.g.dart in your lib folder
4. That's it! Go ahead and use the BuildConfig constants.

{
  "debug": {
    "is_release": false,
    "api_key": "api_key_debug"
  },
  "release": {
    "is_release": true,
    "api_key": "api_key_release"
  }
}

will generate the file build_config.g.dart with the following content if you build for the release varaint.

abstract class BuildConfig {
  static const IS_RELEASE = 'true';
  static const API_KEY = 'api_key_release';
}