AMQP-422 PublisherCallbackChannel: postpone close

JIRA: https://jira.spring.io/browse/AMQP-422

Add `stopSemaphore` and `closeTimeout` option to the `PublisherCallbackChannelImpl`
to postpone physical `close` until timeout or handlong for all pending confirms

Decrease `@Repeat` for `RabbitTemplatePerformanceIntegrationTests` for better build performance
However I think we can overcome this case with `destroying` flag and avoid those `ERROR` message on async channel close, when `connection` is already closed.
WDYT ?