JsonReader char[] leak

The default Json provider ie https://github.com/apache/johnzon is using several pools while parsing eg org.apache.johnzon.max-string-length that wouldn't pool char[] if the JsonReader isn't properly closed.

Currently we're not properly closing such readers and that means that we allocate org.apache.johnzon.max-string-length * 2 bytes on each handled notification ~ 20 MiB.

Until https://bugs.openjdk.java.net/browse/JDK-8027959 ie JDK u40, with G1GC the mentioned char[] was (very likely) allocated into the old generation as Humongous Allocation, needing a Full GC to release it.