Fix RecipientListRouterParser to extend
from AbstractRouterParser, thus eliminating
the problem described in INT-2626.
Previously, the router was a top level bean and, since
it is an @ManagedResource, the mbean exporter eagerly
instantiated it (and its Recipients) before the
ChannelInitializer ran.
Now, it is an anonymous inner bean inside a FB,
so the exporter no longer "finds" it,
thus deferring the Recipient instantiation
until the router itself is instantiated via its FB,
which will be after the C.I. runs.
This is all fine, with one caveat - previously the RLR
is made available as an MBean - now it is not,
unless you ALSO add the int-jmx:mbean-exporter.
However, the MBean is very basic, with no attributes and
a single operation 'setShouldTrack()', so the risk is
extremely low and the workaround is to add the
IntegrationMBeanExporter.
INT-2626 polished based on PR comments
246a202661