build: configure release signing for Android APK

Reads keystore credentials from keystore.properties (gitignored).
Keystore file (myice.keystore) is also gitignored.

composeApp/build.gradle.kts

@@ -1,5 +1,7 @@
 import org.jetbrains.compose.desktop.application.dsl.TargetFormat
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import java.util.Properties
+import java.io.FileInputStream
 
 plugins {
     alias(libs.plugins.kotlin.multiplatform)
@@ -9,6 +11,12 @@ plugins {
     alias(libs.plugins.android.application)
 }
 
+val keystorePropertiesFile = rootProject.file("keystore.properties")
+val keystoreProperties = Properties()
+if (keystorePropertiesFile.exists()) {
+    keystoreProperties.load(FileInputStream(keystorePropertiesFile))
+}
+
 kotlin {
     androidTarget {
         compilations.all {
@@ -86,6 +94,22 @@ android {
         versionName = "1.0"
     }
 
+    signingConfigs {
+        create("release") {
+            keystoreProperties["storeFile"]?.let { storeFile = rootProject.file(it) }
+            storePassword = keystoreProperties["storePassword"] as String?
+            keyAlias = keystoreProperties["keyAlias"] as String?
+            keyPassword = keystoreProperties["keyPassword"] as String?
+        }
+    }
+
+    buildTypes {
+        release {
+            signingConfig = signingConfigs.getByName("release")
+            isMinifyEnabled = false
+        }
+    }
+
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_11
         targetCompatibility = JavaVersion.VERSION_11