Update to Java 11

We should plan to move to Open JDK 11 which is the next LTS release. This issue is meant to track relevant work required to support that

- [ ] Scala - Per current [compatibility][1] matrix JDK 11 looks like still not supported. See scala/scala-dev#559.
- [ ] Akka - Would depend on compatible Scala release
- [ ] Gradle - [Gradle 5.0][2] supports JDK 11

May be its fine to use latest Scala if the JPMS module support is not required. That would need to be validated

[1]: https://docs.scala-lang.org/overviews/jdk-compatibility/overview.html
[2]: https://docs.gradle.org/5.0/release-notes.html#java-11-runtime-support

Start with the Scala JDK compatibility matrix and the linked Gradle 5.0 release notes, then review the Scala, Akka, and Gradle checklist in the issue. Validate whether the relevant Scala and Akka releases support OpenJDK 11 and whether JPMS support is required; done means the required compatibility work is identified and validated.

Written by the indexing model from the issue text.