Upgrade default configuration in ActiveMQ binary distribution

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` ?