Migrate DriveAppFolderViewer with open-source-library-migration guide

[theJawnnybot]

Summary

Applied open-source-library-migration.md to DriveAppFolderViewer.

Build/toolchain

• Java 17
• Gradle 9.3.1 (wrapper + scripts updated)
• AGP 9.1.0
• Kotlin DSL migration (.gradle -> .gradle.kts)
• Dependency updates to current stable versions where appropriate

Publishing

• Added/updated Maven Central publishing via com.vanniktech.maven.publish
• Configured:
  • publishToMavenCentral(SonatypeHost.CENTRAL_PORTAL)
  • signing enabled for release workflow (RELEASE_SIGNING_ENABLED)
• Updated POM metadata in gradle.properties
• Patch bump to VERSION_NAME=5.0.3

CI/CD

• Modernized ci.yml with wrapper validation and Java 17 setup
• Added tag-based publish-release.yml
• Uses tag version arg override (no file mutation):
  • -PVERSION_NAME="${GITHUB_REF_NAME}"
• Uses existing release secrets:
  • MAVEN_CENTRAL_USERNAME
  • MAVEN_CENTRAL_PASSWORD
  • SIGNING_PRIVATE_KEY
  • SIGNING_PASSWORD

Docs/cleanup

• Removed .jitpack.yml and old Groovy publish script
• Updated README with Maven Central badge + dependency snippet
• Added CI badge

Validation

• ./gradlew build ✅
• ./gradlew :driveappfolderviewer:tasks --all includes publish tasks ✅