kamon.Kamon.counter("foo") causes a classloader leak in playframework when using the dev workflow with run.

Here's a minimal project with instructions to reproduce the issue: https://github.com/ornicar/play-cdi-leak/tree/kamon

My setup:

• Linux 5.4.2
• openjdk version "13.0.1" 2019-10-15
• scala 2.13.1
• playframework 2.8.0
• sbt 1.3.5

[edit] Same issue on playframework side: playframework/playframework#9935