inspect: add shell-completion for "--type" flag

With this patch:

    docker inspect --type <TAB>
    config     image    node    secret   task
    container  network  plugin  service  volume

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/system/inspect.go

@@ -39,6 +39,19 @@ const (
 	typeVolume    objectType = "volume"
 )
 
+var allTypes = []objectType{
+	typeConfig,
+	typeContainer,
+	typeImage,
+	typeNetwork,
+	typeNode,
+	typePlugin,
+	typeSecret,
+	typeService,
+	typeTask,
+	typeVolume,
+}
+
 type inspectOptions struct {
 	format     string
 	objectType objectType
@@ -67,6 +80,7 @@ func NewInspectCommand(dockerCli command.Cli) *cobra.Command {
 	flags.StringVar(&opts.objectType, "type", "", "Return JSON for specified type")
 	flags.BoolVarP(&opts.size, "size", "s", false, "Display total file sizes if the type is container")
 
+	_ = cmd.RegisterFlagCompletionFunc("type", completion.FromList(allTypes...))
 	flags.VisitAll(func(flag *pflag.Flag) {
 		// Set a default completion function if none was set. We don't look
 		// up if it does already have one set, because Cobra does this for