Instrumentation for Jetty request handlers

Jetty support is divided into the following sub-modules:

jetty-common:javaagent contains common type instrumentation and advice helper classes used by the javaagent modules of all supported Jetty versions
jetty-8.0:javaagent applies Jetty request handler instrumentation for versions [8, 11)
jetty-11.0:javaagent applies Jetty request handler instrumentation for versions [11,12)
jetty-12.0:javaagent applies Jetty request handler instrumentation for versions [12,)