implemented services unix and npipe complete with test

Signed-off-by: Richard Jones <richard@dagger.io>

tests/plan/context/services/unix/main.cue

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"alpha.dagger.io/dagger/engine"
+	"alpha.dagger.io/docker"
+)
+
+engine.#Plan & {
+	context: services: dockerSocket: unix: "/var/run/docker.sock"
+	actions: nginx: docker.#Run & {
+		ref:  "nginxdemos/nginx-hello"
+		name: "nginx-hello"
+		ports: ["8080:8080"]
+		socket: context.services.dockerSocket.service
+	}
+}