JIRA: https://jira.spring.io/browse/INT-3545
Previously, the `DefaultHeaderChannelRegistry` was auto-started.
This caused the reaper to run and eventually start all the
`taskScheduler` threads, even if the registry was not being used.
- Defer the `start()` until the first channel is stored.
- Do not start the reaper if the bean has been explicitly stopped.
- Deprecate the implementation of `SmartLifecycle`.
Conflicts:
spring-integration-core/src/main/java/org/springframework/integration/channel/DefaultHeaderChannelRegistry.java
Resolved.
__cherry-pick to 3.0.x__
16a081044c