Start Jetty 12 web transactions in the core server's handle function

[obenkenobi]

Web transactions in Jetty 12 only began for apps using servlets. Non-servlet apps using the core Jetty server do not start web transactions.

This is because we start transactions in the Jetty 12 servlet modules.

The core server is instrumented in the jetty-12 instrumentation module. The goal here is to begin transactions in the module using the handle methods there like how they were in our Jetty 11 module.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-259235