Make Java 11 the baseline for Data Prepper

[dlvenable]

Presently the minimum version for running Data Prepper is Java 8. This issue proposes making Java 11 the new minimum. There are a few possible benefits:

• The plugin redesign ([RFC] Plugin Redesign #321) could better use of Java modules which were introduced in Java 9.
• The OpenSearch project has updated to Java 11 as the minimum, including for official clients.
• Fewer versions of Java to test against.
• Make new language features available to contributors and maintainers.

Is running Data Prepper on Java 8 important for you? Please provide feedback.