New metrics to get number of active/waiting connector threads of tomcat

[wbrauneis]

Recently we ran into the situation that our Jira instance had problems responding to web requests. Problem was related to that all tomcat connector threads were in the (time) waiting state. If these metrics data could be exposed, it would help us in better and earlier recognising such a situation.

I am aware of that the thread state is already available for the jvm, however this may include many other unrelated threads as well.