Optimization: Is it possible to add a profile-based constructor?

[yuetchn]

When using etcd, user password authentication is used, but in the current version, I don't see Settings for this part of the configuration, so my current solution is to add a new profile constructor.

The following code is shown:

1.New configuration

type WatcherConfig struct {
	Hosts                []string
	Key                  string `json:",default=casbin_watcher"`
	User                 string
	Pass                 string
	DialKeepAliveTimeout time.Duration `json:",default=10"`
	DialTimeout          time.Duration `json:",default=30"`
}

2.Added configuration-based constructors

// NewWatcherWithConfig is a configurable Watcher constructor
func NewWatcherWithConfig(config WatcherConfig) (persist.Watcher, error) {
	w := &Watcher{}
	w.running = true
	w.callback = nil
	w.conf = &config

	// Create the client.
	err := w.createClient()
	if err != nil {
		return nil, err
	}

	// Call the destructor when the object is released.
	runtime.SetFinalizer(w, finalizer)

	go func() {
		_ = w.startWatch()
	}()

	return w, nil
}

3.Adjust the createClient method

func (w *Watcher) createClient() error {
	cfg := client.Config{
		Endpoints: w.endpoints,
		// set timeout per request to fail fast when the target endpoints is unavailable
		DialKeepAliveTimeout: time.Second * 10,
		DialTimeout:          time.Second * 30,
		Password:             w.password,
	}

	if w.conf != nil {
		cfg = client.Config{
			Endpoints: w.conf.Hosts,
			// set timeout per request to fail fast when the target endpoints is unavailable
			DialTimeout:          time.Second * w.conf.DialTimeout,
			DialKeepAliveTimeout: time.Second * w.conf.DialKeepAliveTimeout,
			Username:             w.conf.User,
			Password:             w.conf.Pass,
		}
	}

	c, err := client.New(cfg)
	if err != nil {
		return err
	}
	w.client = c
	return nil
}

[hsluoyz]

@yuetchn sounds good to me. Can you make a PR to add it?

[yuetchn]

@yuetchn sounds good to me. Can you make a PR to add it?
the relevant PR has been submitted.
#25