Initial Beta Release to support plugin development

• Requires Gradle 7 and later
• Supports building on JDK 16
• Initial plugin support using the plugin JVM driver library (WIP)

Changelog:

• feat(V4): Implemented models for Synchronous Message interactions
• chore: Upgrade kotlin-result and kotlin-logging
• feat(plugins): support generating content via plugin
• chore: Upgrade HTTP client to 5.1
• feat(plugins): implemented support for content matchers via plugins
• chore: first phase of changes to support plugins
• chore: upgrade KTor to 1.6.1
• feat: Introduce PactBuilder DSL class (will be able to apply plugins)
• chore: Upgrade Kotlin to 1.5.21
• chore: remove deprecated methods
• chore: got the build working with JDK 16
• chore: Upgrade Gradle to 7.1.1