INT-2426: Add `Idempotent Receiver` EIP pattern

JIRA: https://jira.spring.io/browse/INT-2426

**DO NOT MERGE YET**

It's just an initial commit, like a PoC to review before further work.
I understand what you are doing here but when `skipDuplicate` is false this is really a transformer not a filter.

It makes me feel a bit queasy. 

Maybe we can work around it with the namespace ?

    <int:idempotent-consumer filter="true|false" />

rather than `<idempotent-filter/>` as mentioned in the JIRA.