GH-1720: Default Property Doc Improvements
GH-1720: Default Property Doc Improvements

Fixes https://github.com/spring-cloud/spring-cloud-stream/issues/1720
Resolves #1724

garyrussell/spring-cloud-stream,spring-cloud/spring-cloud-stream,spring-cloud/spring-cloud-stream,garyrussell/spring-cloud-stream,ilayaperumalg/spring-cloud-stream,ilayaperumalg/spring-cloud-stream,garyrussell/spring-cloud-stream,spring-cloud/spring-cloud-stream