monitor core sessions (leaks investigation) and rename monitors

JTAJCA management gives helpful information about sessions, connections and transactions pools. We want them to be published in the same manner as the metrics. Here is the published monitor's names

• org.nuxeo.ecm.core.management.jtajca:type=ConnectionMonitor,name=repository
• org.nuxeo.ecm.core.management.jtajca:type=TransactionMonitor,name=jdoe
• org.nuxeo.ecm.core.management.jtajca:type=CoreSessionMonitor,name=jdoe

Note: the CoreSessionMonitor was introduced in this ticket for tracking the session creation contexts. This is useful for investigating session leaks.