[ECO-5020] fix: update AGP plugin

- updated AGP plugin to 8.0
- added build config feature
- added support for older AGP versions

android/build.gradle

@@ -8,7 +8,7 @@ buildscript {
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:7.2.0'
+        classpath 'com.android.tools.build:gradle:8.0.0'
     }
 }
 
@@ -35,6 +35,11 @@ dependencies {
 android {
     compileSdkVersion 32
 
+    // Conditional for compatibility with AGP <4.2.
+    if (project.android.hasProperty("namespace")) {
+        namespace 'io.ably.flutter.plugin'
+    }
+
     // Require Java language level 8 so we can use Method References (used with Lambdas)
     compileOptions {
         sourceCompatibility JavaVersion.VERSION_1_8
@@ -56,6 +61,9 @@ android {
     lintOptions {
         disable 'InvalidPackage'
     }
+    buildFeatures {
+        buildConfig true
+    }
 }
 
 apply from: file("./ably-agent.gradle")