INTEXT-104: Add ability to set order for kafka outbound channel adapter

order attribute now honored if kafka outbound adapter is connected to a subscribable channel
unit tests and samples are updated
OK. That's good.
However whould be better to use `<xsd:attributeGroup ref="integration:channelAdapterAttributes"/>` for `auto-startup` and phase.
The `id` and `channel` attributes should be removed from here, respectively.

Please, make this XSD based on `schemaLocation="http://www.springframework.org/schema/integration/spring-integration-4.0.xsd"`.
Not all IDE can resolve XSD imports using `spring.schemas`