* Add 'trace_flags' to logging MDC
* Remove 'sampled' flag
* Rename MDC keys to the current logging spec convention: trace_id instead of traceId
* Fix smoke tests
* testing-common refactoring: replace direct AgentTestRunner usage with spock spec
* Updated instrumentation docs
* Fix reactor-core library tests
ReactorCoreTest was getting a tracer from GlobalOpenTelemetry before LibraryTestTrait had a change to initialize the SDK