* Use spotless for formatting / license check
* Apply formatting
* README
* Apply to example
* google-java-format 1.8 for now
* google-java-format 1.7 for now (last supporting Java 8)
* Extension packages should not use "internal" API package
Add InternalApiProtectionTest which uses ArchUnit to enforce architectural constraints.
This change only verifies that classes in `extensions` packages do not use classes in `internal` package of API module.
Test was added into `opentelemetry-all` module because the latter depends on all other submodules
and therefore sees all classes in the project.
* Polish
* Polish