Add a common interface between different Kubernetes Stack API versions and use it in kubernetes stack commands

* Add kubernetes Stack API v1beta2 client
* Upgrade v1beta1 client to remove generated code

Signed-off-by: Silvin Lubecki <silvin.lubecki@docker.com>

cli/command/stack/kubernetes/stackclient_test.go

@@ -0,0 +1,39 @@
+package kubernetes
+
+import (
+	"testing"
+
+	composetypes "github.com/docker/cli/cli/compose/types"
+	"github.com/gotestyourself/gotestyourself/assert"
+)
+
+func TestFromCompose(t *testing.T) {
+	stackClient := &stackV1Beta1{}
+	s, err := stackClient.FromCompose("foo", composetypes.Config{
+		Version:  "3.1",
+		Filename: "banana",
+		Services: []composetypes.ServiceConfig{
+			{
+				Name:  "foo",
+				Image: "foo",
+			},
+			{
+				Name:  "bar",
+				Image: "bar",
+			},
+		},
+	})
+	assert.NilError(t, err)
+	assert.Equal(t, "foo", s.name)
+	assert.Equal(t, string(`version: "3.1"
+services:
+  bar:
+    image: bar
+  foo:
+    image: foo
+networks: {}
+volumes: {}
+secrets: {}
+configs: {}
+`), s.composeFile)
+}