5.1.0.M2 (Milestone)

Change log:

9be9e63 Upgrade to Spring AMQP 2.1 M2
0f27a9f Upgrade to Reactor 3.2 M4, R-Netty- 0.8 M2
f403dd5 Upgrade Spring Dependencies
595ef3a INT-4519: JmsTests Polishing
0545a7b INT-4519: Improve JMS inbound-c-a receiveTimeout (#2540)
f9fe709 Add Java DSL .fluxTransform(Function) operator (#2541)
e053e2a INT-4524: Fix MailReceivingMessageSource BF usage
8f639ad Move LeaderInitiators to later phase
5e47a6a INT-4517: Refactor beans in IntegrationRegistrar (#2537)
60db7bc INT-4518: Channel late-binding in Messaging Anns
e2b398a Adapt to the latest Reactor
a4ffddf Upgrade to latest B-S of all Spring dependencies
26229c9 INT-4480: Use component type for ids in the flow (#2536)
055e9a4 INT-4457: Add logAndReply() terminal operator
4a85849 INT-3364: Add batchUpdate into JdbcMessageHandler (#2534)
34ac66d Ignore the Aggregator Performance test
23a3462 Add @NonNullApi where appropriate
03a3bbb More JDBC doc fixes