XWIKI-11486: Batch API to send large volumes of mail

* Create xwiki-platform-mail-send-batch module structure
* Create iterators (GroupMimeMessageIterator, UsersMimeMessageIterator, SerializedFilesMimeMessageIterator)
Actually that's not correct either. I think we need to modify the Component annotation to accept Type instead of Class and check if we can reference a generic from there using the DefaultParametrizedType class