Example of overriding an apk name with custom values and signed or unsigned suffix.

build.gradle

applicationVariants.all { variant ->
    variant.outputs.all {
        outputFileName =
                "${project.name.toLowerCase()}-" +               // app
                "${variant.flavorName}-" +                       // develop
                "${variant.buildType.name}-" +                   // debug
                "${versionCode}" +                               // 10101
                 (variant.buildType.name.contains("release")
                 && !variant.signingReady ? "-unsigned" : "") +  // unsigned
                        
                ".apk"    // i.e.: app-develop-debug-10101-unsigned.apk
    }
}