How to create a release signed apk file using Gradle?

I would like to have my Gradle build to create a release signed apk file using Gradle.

I'm not sure if the code is correct or if I'm missing a parameter when doing gradle build?

This is some of the code in my build.gradle/build.gradle.kts file:

android {
    ...
    signingConfigs {
        release {
            storeFile(file("release.keystore"))
            storePassword("******")
            keyAlias("******")
            keyPassword("******")
        }
    }
}

The Gradle build finishes SUCCESSFUL, and in my build/apk folder I only see the ...-release-unsigned.apk and ...-debug-unaligned.apk files.

Any suggestions on how to solve this?

Easier way than previous answers:

Put this into ~/.gradle/gradle.properties

RELEASE_STORE_FILE={path to your keystore}
RELEASE_STORE_PASSWORD=*****
RELEASE_KEY_ALIAS=*****
RELEASE_KEY_PASSWORD=*****

Modify your app/build.gradle, and add this inside the android { code block:

...    
signingConfigs {

   release {
       storeFile file(RELEASE_STORE_FILE)
       storePassword RELEASE_STORE_PASSWORD
       keyAlias RELEASE_KEY_ALIAS
       keyPassword RELEASE_KEY_PASSWORD

       // Optional, specify signing versions used
       v1SigningEnabled true
       v2SigningEnabled true
   }
}

buildTypes {
        release {
            signingConfig signingConfigs.release
        }
}
....

Then you can run gradle assembleRelease

Also see the reference for the signingConfigs Gradle DSL