This adds a recipe for window-management-client-grpc for testing out the
gRPC interface. This client will talk with the compositor indirectly,
using the gRPC interface exposed by the grpc-proxy helper client.
Bug-AGL: SPEC-4673
Change-Id: Ib1a9d14a3bd41ea64180494962f97f0d5b557c09 Signed-off-by: Marius Vlad <marius.vlad@collabora.com>