Callback listener for inbound and outbound Session migration.
A Session is preemptively moved between its associated set of SessionManagers. For instance, when a
ClusteredInvocation for a given Session is invoked on a Node where the local SessionManager, RequestingSM, does not
own the targeted Session, the SessionManager owning the Session, OwningSM, the Session may be moved from OwningSM
to RequestingSM. OwningSM, prior to relinquish the Session, executes notifyOutboundSessionMigration and provides
the Session under migration. RequestingRM, after having acquired the Session ownership, executes
notifyInboundSessionMigration and provides the Session under migration.
The typical usage of these migration callbacks are to allow a wrapping SessionManager, e.g. an HTTPSession manager,
to perform bookkeeping operations.