Upgrade build dependencies for the project

- Upgrade to Gradle 8.11
- Upgrade to Android Gradle Plugin 8.7.2
- Remove deprecated android.defaults.buildfeatures.buildconfig=true
  gradle property, it is not needed as mastodon/build.gradle already
  sets android { buildFeatures { buildConfig true } }
- Move plugin repository definition to settings.gradle to match latest
  Gradle practices
- Move to using plugin {} mechanism to add Android Gradle Plugin to
  match the latest Gradle practices
- Remove root project clean task as this project does not produce any
  real artifacts, it seems to be leftover from original Android new
  project template

settings.gradle

@@ -1,3 +1,16 @@
+pluginManagement {
+	repositories {
+		google()
+		mavenCentral()
+		maven {
+			url "https://www.jitpack.io"
+			content {
+				includeModule 'com.github.UnifiedPush', 'android-connector'
+			}
+		}
+		mavenLocal()
+	}
+}
 dependencyResolutionManagement {
 	repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
 	repositories {