Upgrade default configuration in ActiveMQ binary distribution

[jbonofre]

The default ActiveMQ configuration is pretty "low" in the binary distribution:

• in bin/setenv:
  • the default ACTIVEMQ_OPTS_MEMORY should be updated to a more modern configuration, for instance using -XX:AutoBoxCacheMax=20000 -XX:+PrintClassHistogram -XX:+UseG1GC -XX:+UseStringDeduplication -Xms512M -Xmx2G
• the conf/activemq.xml should be updated by default:
  • should we keep the contantPendingMessageLimitStrategy in destination policies by default ?
  • should we add prefetch configuration in destination policies (for visibility) ?
  • should we add kahaDB tuning by default (checkForCorruptJournalFiles, indexCacheSize, indexWriteBatchSize, journalMaxFileLength, maxAsyncJobs, ...). The purpose is not to change the default values in the code, it's really to "expose" this configuration in the default activemq.xml to our users.
  • change the default systemUsage ?