Simplify the marshaling of compose types.Config

- Add `Version` to `types.Config`
- Add a new `Services` types (that is just `[]ServiceConfig`) and add
  `MarshalYAML` method on it.
- Clean other top-level custom marshaling as `Services` is the only one
  required.

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

cli/command/stack/swarm/deploy_composefile.go

@@ -18,7 +18,7 @@ import (
 )
 
 func deployCompose(ctx context.Context, dockerCli command.Cli, opts options.Deploy) error {
-	config, _, err := loader.LoadComposefile(dockerCli, opts)
+	config, err := loader.LoadComposefile(dockerCli, opts)
 	if err != nil {
 		return err
 	}