in generator.go [133:143]
func (config *FluentConfigGenerator) AddFieldToRecord(key string, value string, tag string) FluentConfig {
_, ok := config.ModifyRecords[tag]
if !ok {
config.ModifyRecords[tag] = RecordModifier{
NewFields: make(map[string]string),
}
}
config.ModifyRecords[tag].NewFields[key] = value
return config
}