title: Add support for AS2 adapters
body: <p>May I know is there any plan for Spring integration to support AS2?
  I found this thread however seems there is no conclusion about AS2, thanks
  <a href="https://jira.spring.io/browse/SESIA-17" rel="nofollow noreferrer">https://jira.spring.io/browse/SESIA-17</a></p>