INT-2352 Support Control-Bus Atomic Router Updates

JIRA: https://jira.spring.io/browse/INT-2352

Add `replaceChannelMappings()` to the `AMMR`.

INT-2352 Polishing - PR Comments

Consolidate tests.
Fix up `@ManagedAttribute` Vs `@ManagedOperation`
Expose `setChannelMappings` over JMX