fix:config groutine(watch) leak (#1327)

* fix:config goroutine(watch) Leak

config/env/watcher.go

@@ -1,24 +1,37 @@
 package env
 
 import (
+	"context"
+
 	"github.com/go-kratos/kratos/v2/config"
 )
 
 type watcher struct {
 	exit chan struct{}
+
+	ctx    context.Context
+	cancel context.CancelFunc
 }
 
+var _ config.Watcher = (*watcher)(nil)
+
 func NewWatcher() (config.Watcher, error) {
-	return &watcher{exit: make(chan struct{})}, nil
+	ctx, cancel := context.WithCancel(context.Background())
+	return &watcher{exit: make(chan struct{}), ctx: ctx, cancel: cancel}, nil
 }
 
 // Next will be blocked until the Stop method is called
 func (w *watcher) Next() ([]*config.KeyValue, error) {
-	<-w.exit
-	return nil, nil
+	select {
+	case <-w.ctx.Done():
+		return nil, w.ctx.Err()
+	case <-w.exit:
+		return nil, nil
+	}
 }
 
 func (w *watcher) Stop() error {
 	close(w.exit)
+	w.cancel()
 	return nil
 }