Integrate Android example

[Nashatyrev]

Adds Android example to the gradle build to ensure jvm-Libp2p is interoperable with Android SDK:

• Upgrade Gradle version to 8.0
• Refactor Android example
• Add 2 Android gradle plugins (without applying) to the root build (haven't managed to isolate them in Android example module)
• Add android.useAndroidX property to the root gradle.properties (for some reason defining this property in the Android submodule doesn't work)
• Add libp2p.gradle.custom per project property which indicates whether common gradle code for submodules should be skipped (set it up for Adnroid example)
• Move Maven repositories definitions to settings.gradle
• In the settings.gradle detect if Android SDK is installed and conditionally include :examples:android-chatter module
  • check if env var ANDROID_HOME is defined
  • or sdk.dir property is defined in local.properties file (created by AndroidStudio)
• Add Setup Android SDK GitHub action

As a result:

• When no Android SDK is installed:
  • Gradle build works as before, Android example is not included into the build
  • The project is imported into IntelliJ IDEA as before: Android example is not included as a module
• When Android SDK is installed and env var ANDROID_HOME is defined, Android example is build by the gradle
• When the project is imported to AndroidStudio (local.properties file is automatically created), the Android example module is included and can be executed

Fix #270

[StefanBratanov]

LGTM

[Nashatyrev]

Part of #272