GH-3555: Change logger order for errorChannel (#3949)

* GH-3555: Change logger order for errorChannel

Fixes https://github.com/spring-projects/spring-integration/issues/3555

The default global `errorChannel` has a `LoggingHandler` as a subscriber.
It is subscribed without any `order` which may lose logging messages,
when another subscriber with re-throw is present.

* Set default `LoggingHandler` on the default `errorChannel` to `Ordered.LOWEST_PRECEDENCE - 100`
to give a room for custom subscribers without an `order` and still get error logged

* Add extra note in docs about an order for custom subcribers

Co-authored-by: Gary Russell <grussell@vmware.com>

Co-authored-by: Gary Russell <grussell@vmware.com>

src/reference/asciidoc/error-handling.adoc

@@ -52,6 +52,8 @@ QueueChannel errorChannel() {
 ====
 
 NOTE: The default error channel is a `PublishSubscribeChannel`.
+By default, it has a `LoggingHandler` as a subscriber with an `ERROR` logging level and subscription order as `Ordered.LOWEST_PRECEDENCE - 100`.
+If you subscribe additional consuming endpoints, that might throw an exception, and you don't want to preempt the logging, ensure that the additional handlers have a higher order.
 
 The most important thing to understand here is that the messaging-based error handling applies only to exceptions that are thrown by a Spring Integration task that is executing within a `TaskExecutor`.
 This does not apply to exceptions thrown by a handler that operates within the same thread as the sender (for example, through a `DirectChannel` as described earlier in this section).