INT-3657: Default MaxMessPerPoll=1 for @InboundCA

JIRA: https://jira.spring.io/browse/INT-3657

With XML/DSL, the MMPP defaults to 1 (via the SPCAFB) but
@InboundChannelAdapter defaulted to -1 (infinity).

Change the annotation to be consistent with the XML/DSL.

Add missing schema docs for the `basePollerType`.

* Fix `AbstractMethodAnnotationPostProcessor` for `maxMessagesPerPollValue` override
* Change `EnableIntegrationTests#foo()` `@InboundChannelAdapter` to use `maxMessagesPerPoll = "2"`
and modify appropriate test-case to be sure that `maxMessagesPerPoll` isn't overriden as it has been done in the original commit.

build.gradle

@@ -195,6 +195,7 @@ subprojects { subproject ->
 	}
 
 	test {
+		maxHeapSize = "1024m"
 		jvmArgs "-javaagent:${configurations.jacoco.asPath}=destfile=${buildDir}/jacoco.exec,includes=org.springframework.integration.*"
 	}