Extract scaling from zero

- extracting this package means it can be used in other components
such as the asynchronous nats-queue-worker which may need to
invoke functions which are scaled down to zero replicas.

Ref: https://github.com/openfaas/nats-queue-worker/issues/32

Tested on Docker Swarm for scaling up, already scaled and not
found error.

Signed-off-by: Alex Ellis (VMware) <alexellis2@gmail.com>

gateway/Dockerfile.arm64

@@ -13,6 +13,7 @@ COPY tests          tests
 COPY types          types
 COPY queue          queue
 COPY plugin         plugin
+COPY scaling        scaling
 COPY server.go      .
 
 # Run a gofmt and exclude all vendored code.