This commit documents the fact that the Servlet Filter based
observations for MVC applications is limited by the Servlet Filter
contract in the first place. All processing and logging that happens
outside of the scope of the filter is not observed.
Log statements from the catalina engine (in the case of Tomcat), or any
container-specific infrastructure, is not covered by the
instrumentation.
Closes gh-29398
Sam Brannen
Brian Clozel
Stephane Nicoll
Rob Winch