build: updates to build and test with LTS JDKs

[codefromthecrypt]

This updates to build and test with LTS JDKs, using the same project setup as zipkin and zipkin-reporter

• moves off takari to normal maven wrapper, and updates all plugin versions
• removes retrolambda which is incompatible with recent JDKs
  • ports java 6 code to java 6 syntax
  • test release profile with JDK 11, which is last to compile java 1.6.
• adds opens configuration for old spring and grpc integration tests
• moves off abandoned powermock for mockito
  • bytebuddy no longer supports mocking System, so had to refactor code around currentTime
• updates GitHub Actions to build on first and last LTS (11, 21)
  • adds javadoc tests to ensure it will build prior to running deploy job

[codefromthecrypt]

going to merge to get jupiter started, as bumping all this stuff is prereq to re-cutting zipkin-aws and zipkin-gcp