Fixes: #9863
Issue link: https://github.com/spring-projects/spring-integration/issues/9863
The `PollerMetadata.sendTimeout` has been migrated to the `SourcePollingChannelAdapter.setSendTimeout()` long time ago.
Right now this option is not propagated anywhere
* Introduce missed `SourcePollingChannelAdapterSpec.sendTimeout`
* Deprecate (for removal) `PollerMetadata.sendTimeout`
* Verify `SourcePollingChannelAdapterSpec.sendTimeout` option in the `ReactiveStreamsTests`
(cherry picked from commit 0af3b25cd6)