[AMQ7,JMX] Some destination JMX statistics do not take into account only the current held messages

Destination JMX statistics to monitor the queues of the broker but some parameters are computed since last boot or statistics reset. For example MaxEnqueueTime and MinEnqueueTime are two statistics relative not the current messages held but to the overall messages that sat in the destination.

Currently we need to force the statistics reset in order to reset the Max and Min values. It would be useful to have two additional statistics like "CurrentMaxEnqueueTime and CurrentMinEnqueueTime" or something similar.