pkg/jsonmessage: export "Stream" interface
pkg/jsonmessage: export "Stream" interface

This interface is used as part of an exported function's signature,
so exporting the interface as well for callers to know what the argument
must have implemented.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

cpuguy83/docker,Mokolea/docker,trebonian/docker,Mokolea/docker,Mokolea/docker,Mokolea/docker,moul/docker,Ramzec/docker,moby/moby,thaJeztah/docker,thaJeztah/docker,moul/docker,trebonian/docker,moby/moby,konstruktoid/docker-upstream,konstruktoid/docker-upstream,konstruktoid/docker-upstream,jimjag/docker,thaJeztah/docker,mahak/docker,mahak/docker,moul/docker,cpuguy83/docker,thaJeztah/docker,jimjag/docker,trebonian/docker,jimjag/docker,konstruktoid/docker-upstream,cpuguy83/docker,moby/moby,moby/moby,moul/docker,Ramzec/docker,mahak/docker,jimjag/docker,Ramzec/docker,mahak/docker,Ramzec/docker,trebonian/docker,cpuguy83/docker