[Task]: Build with newer Java to keep up Gradle plugins and build health (still target Java 8 compatibility for released artifacts)

[kennknowles]

What needs to happen?

Many gradle plugins and toolchains (like spotless, errorprone) are dropping Java 8 support. We still need to allow users of Java 8 to use Beam but we don't need to run Gradle with Java 8.

Issue Priority

Priority: 2 (default / most normal work should be filed as P2)

Issue Components

• [ ] Component: Python SDK
• [ ] Component: Java SDK
• [ ] Component: Go SDK
• [ ] Component: Typescript SDK
• [ ] Component: IO connector
• [ ] Component: Beam YAML
• [ ] Component: Beam examples
• [ ] Component: Beam playground
• [ ] Component: Beam katas
• [ ] Component: Website
• [ ] Component: Spark Runner
• [ ] Component: Flink Runner
• [ ] Component: Samza Runner
• [ ] Component: Twister2 Runner
• [ ] Component: Hazelcast Jet Runner
• [ ] Component: Google Cloud Dataflow Runner