android {
    
    ....
    
    applicationVariants.all { variant ->
        variant.outputs.all { output ->
            def date = new Date()
            def formattedDate = date.format('yyMMdd')
            def newApkName = "${appName}_${variant.flavorName}_${variant.versionCode}_${formattedDate}.apk"

            outputFileName = newApkName
        }
    }
}

샘플 소스 github